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| H A D | dynroot.c | diff 92e3cc91 Fri Oct 09 07:11:58 MDT 2020 David Howells <dhowells@redhat.com> afs: Fix rapid cell addition/removal by not using RCU on cells tree There are a number of problems that are being seen by the rapidly mounting and unmounting an afs dynamic root with an explicit cell and volume specified (which should probably be rejected, but that's a separate issue): What the tests are doing is to look up/create a cell record for the name given and then tear it down again without actually using it to try to talk to a server. This is repeated endlessly, very fast, and the new cell collides with the old one if it's not quick enough to reuse it. It appears (as suggested by Hillf Danton) that the search through the RB tree under a read_seqbegin_or_lock() under RCU conditions isn't safe and that it's not blocking the write_seqlock(), despite taking two passes at it. He suggested that the code should take a ref on the cell it's attempting to look at - but this shouldn't be necessary until we've compared the cell names. It's possible that I'm missing a barrier somewhere. However, using an RCU search for this is overkill, really - we only need to access the cell name in a few places, and they're places where we're may end up sleeping anyway. Fix this by switching to an R/W semaphore instead. Additionally, draw the down_read() call inside the function (renamed to afs_find_cell()) since all the callers were taking the RCU read lock (or should've been[*]). [*] afs_probe_cell_name() should have been, but that doesn't appear to be involved in the bug reports. The symptoms of this look like: general protection fault, probably for non-canonical address 0xf27d208691691fdb: 0000 [#1] PREEMPT SMP KASAN KASAN: maybe wild-memory-access in range [0x93e924348b48fed8-0x93e924348b48fedf] ... RIP: 0010:strncasecmp lib/string.c:52 [inline] RIP: 0010:strncasecmp+0x5f/0x240 lib/string.c:43 afs_lookup_cell_rcu+0x313/0x720 fs/afs/cell.c:88 afs_lookup_cell+0x2ee/0x1440 fs/afs/cell.c:249 afs_parse_source fs/afs/super.c:290 [inline] ... Fixes: 989782dcdc91 ("afs: Overhaul cell database management") Reported-by: syzbot+459a5dce0b4cb70fd076@syzkaller.appspotmail.com Signed-off-by: David Howells <dhowells@redhat.com> cc: Hillf Danton <hdanton@sina.com> cc: syzkaller-bugs@googlegroups.com diff 92e3cc91 Fri Oct 09 07:11:58 MDT 2020 David Howells <dhowells@redhat.com> afs: Fix rapid cell addition/removal by not using RCU on cells tree There are a number of problems that are being seen by the rapidly mounting and unmounting an afs dynamic root with an explicit cell and volume specified (which should probably be rejected, but that's a separate issue): What the tests are doing is to look up/create a cell record for the name given and then tear it down again without actually using it to try to talk to a server. This is repeated endlessly, very fast, and the new cell collides with the old one if it's not quick enough to reuse it. It appears (as suggested by Hillf Danton) that the search through the RB tree under a read_seqbegin_or_lock() under RCU conditions isn't safe and that it's not blocking the write_seqlock(), despite taking two passes at it. He suggested that the code should take a ref on the cell it's attempting to look at - but this shouldn't be necessary until we've compared the cell names. It's possible that I'm missing a barrier somewhere. However, using an RCU search for this is overkill, really - we only need to access the cell name in a few places, and they're places where we're may end up sleeping anyway. Fix this by switching to an R/W semaphore instead. Additionally, draw the down_read() call inside the function (renamed to afs_find_cell()) since all the callers were taking the RCU read lock (or should've been[*]). [*] afs_probe_cell_name() should have been, but that doesn't appear to be involved in the bug reports. The symptoms of this look like: general protection fault, probably for non-canonical address 0xf27d208691691fdb: 0000 [#1] PREEMPT SMP KASAN KASAN: maybe wild-memory-access in range [0x93e924348b48fed8-0x93e924348b48fedf] ... RIP: 0010:strncasecmp lib/string.c:52 [inline] RIP: 0010:strncasecmp+0x5f/0x240 lib/string.c:43 afs_lookup_cell_rcu+0x313/0x720 fs/afs/cell.c:88 afs_lookup_cell+0x2ee/0x1440 fs/afs/cell.c:249 afs_parse_source fs/afs/super.c:290 [inline] ... Fixes: 989782dcdc91 ("afs: Overhaul cell database management") Reported-by: syzbot+459a5dce0b4cb70fd076@syzkaller.appspotmail.com Signed-off-by: David Howells <dhowells@redhat.com> cc: Hillf Danton <hdanton@sina.com> cc: syzkaller-bugs@googlegroups.com |
| H A D | main.c | diff 92e3cc91 Fri Oct 09 07:11:58 MDT 2020 David Howells <dhowells@redhat.com> afs: Fix rapid cell addition/removal by not using RCU on cells tree There are a number of problems that are being seen by the rapidly mounting and unmounting an afs dynamic root with an explicit cell and volume specified (which should probably be rejected, but that's a separate issue): What the tests are doing is to look up/create a cell record for the name given and then tear it down again without actually using it to try to talk to a server. This is repeated endlessly, very fast, and the new cell collides with the old one if it's not quick enough to reuse it. It appears (as suggested by Hillf Danton) that the search through the RB tree under a read_seqbegin_or_lock() under RCU conditions isn't safe and that it's not blocking the write_seqlock(), despite taking two passes at it. He suggested that the code should take a ref on the cell it's attempting to look at - but this shouldn't be necessary until we've compared the cell names. It's possible that I'm missing a barrier somewhere. However, using an RCU search for this is overkill, really - we only need to access the cell name in a few places, and they're places where we're may end up sleeping anyway. Fix this by switching to an R/W semaphore instead. Additionally, draw the down_read() call inside the function (renamed to afs_find_cell()) since all the callers were taking the RCU read lock (or should've been[*]). [*] afs_probe_cell_name() should have been, but that doesn't appear to be involved in the bug reports. The symptoms of this look like: general protection fault, probably for non-canonical address 0xf27d208691691fdb: 0000 [#1] PREEMPT SMP KASAN KASAN: maybe wild-memory-access in range [0x93e924348b48fed8-0x93e924348b48fedf] ... RIP: 0010:strncasecmp lib/string.c:52 [inline] RIP: 0010:strncasecmp+0x5f/0x240 lib/string.c:43 afs_lookup_cell_rcu+0x313/0x720 fs/afs/cell.c:88 afs_lookup_cell+0x2ee/0x1440 fs/afs/cell.c:249 afs_parse_source fs/afs/super.c:290 [inline] ... Fixes: 989782dcdc91 ("afs: Overhaul cell database management") Reported-by: syzbot+459a5dce0b4cb70fd076@syzkaller.appspotmail.com Signed-off-by: David Howells <dhowells@redhat.com> cc: Hillf Danton <hdanton@sina.com> cc: syzkaller-bugs@googlegroups.com diff 92e3cc91 Fri Oct 09 07:11:58 MDT 2020 David Howells <dhowells@redhat.com> afs: Fix rapid cell addition/removal by not using RCU on cells tree There are a number of problems that are being seen by the rapidly mounting and unmounting an afs dynamic root with an explicit cell and volume specified (which should probably be rejected, but that's a separate issue): What the tests are doing is to look up/create a cell record for the name given and then tear it down again without actually using it to try to talk to a server. This is repeated endlessly, very fast, and the new cell collides with the old one if it's not quick enough to reuse it. It appears (as suggested by Hillf Danton) that the search through the RB tree under a read_seqbegin_or_lock() under RCU conditions isn't safe and that it's not blocking the write_seqlock(), despite taking two passes at it. He suggested that the code should take a ref on the cell it's attempting to look at - but this shouldn't be necessary until we've compared the cell names. It's possible that I'm missing a barrier somewhere. However, using an RCU search for this is overkill, really - we only need to access the cell name in a few places, and they're places where we're may end up sleeping anyway. Fix this by switching to an R/W semaphore instead. Additionally, draw the down_read() call inside the function (renamed to afs_find_cell()) since all the callers were taking the RCU read lock (or should've been[*]). [*] afs_probe_cell_name() should have been, but that doesn't appear to be involved in the bug reports. The symptoms of this look like: general protection fault, probably for non-canonical address 0xf27d208691691fdb: 0000 [#1] PREEMPT SMP KASAN KASAN: maybe wild-memory-access in range [0x93e924348b48fed8-0x93e924348b48fedf] ... RIP: 0010:strncasecmp lib/string.c:52 [inline] RIP: 0010:strncasecmp+0x5f/0x240 lib/string.c:43 afs_lookup_cell_rcu+0x313/0x720 fs/afs/cell.c:88 afs_lookup_cell+0x2ee/0x1440 fs/afs/cell.c:249 afs_parse_source fs/afs/super.c:290 [inline] ... Fixes: 989782dcdc91 ("afs: Overhaul cell database management") Reported-by: syzbot+459a5dce0b4cb70fd076@syzkaller.appspotmail.com Signed-off-by: David Howells <dhowells@redhat.com> cc: Hillf Danton <hdanton@sina.com> cc: syzkaller-bugs@googlegroups.com |
| H A D | cell.c | diff 92e3cc91 Fri Oct 09 07:11:58 MDT 2020 David Howells <dhowells@redhat.com> afs: Fix rapid cell addition/removal by not using RCU on cells tree There are a number of problems that are being seen by the rapidly mounting and unmounting an afs dynamic root with an explicit cell and volume specified (which should probably be rejected, but that's a separate issue): What the tests are doing is to look up/create a cell record for the name given and then tear it down again without actually using it to try to talk to a server. This is repeated endlessly, very fast, and the new cell collides with the old one if it's not quick enough to reuse it. It appears (as suggested by Hillf Danton) that the search through the RB tree under a read_seqbegin_or_lock() under RCU conditions isn't safe and that it's not blocking the write_seqlock(), despite taking two passes at it. He suggested that the code should take a ref on the cell it's attempting to look at - but this shouldn't be necessary until we've compared the cell names. It's possible that I'm missing a barrier somewhere. However, using an RCU search for this is overkill, really - we only need to access the cell name in a few places, and they're places where we're may end up sleeping anyway. Fix this by switching to an R/W semaphore instead. Additionally, draw the down_read() call inside the function (renamed to afs_find_cell()) since all the callers were taking the RCU read lock (or should've been[*]). [*] afs_probe_cell_name() should have been, but that doesn't appear to be involved in the bug reports. The symptoms of this look like: general protection fault, probably for non-canonical address 0xf27d208691691fdb: 0000 [#1] PREEMPT SMP KASAN KASAN: maybe wild-memory-access in range [0x93e924348b48fed8-0x93e924348b48fedf] ... RIP: 0010:strncasecmp lib/string.c:52 [inline] RIP: 0010:strncasecmp+0x5f/0x240 lib/string.c:43 afs_lookup_cell_rcu+0x313/0x720 fs/afs/cell.c:88 afs_lookup_cell+0x2ee/0x1440 fs/afs/cell.c:249 afs_parse_source fs/afs/super.c:290 [inline] ... Fixes: 989782dcdc91 ("afs: Overhaul cell database management") Reported-by: syzbot+459a5dce0b4cb70fd076@syzkaller.appspotmail.com Signed-off-by: David Howells <dhowells@redhat.com> cc: Hillf Danton <hdanton@sina.com> cc: syzkaller-bugs@googlegroups.com diff 92e3cc91 Fri Oct 09 07:11:58 MDT 2020 David Howells <dhowells@redhat.com> afs: Fix rapid cell addition/removal by not using RCU on cells tree There are a number of problems that are being seen by the rapidly mounting and unmounting an afs dynamic root with an explicit cell and volume specified (which should probably be rejected, but that's a separate issue): What the tests are doing is to look up/create a cell record for the name given and then tear it down again without actually using it to try to talk to a server. This is repeated endlessly, very fast, and the new cell collides with the old one if it's not quick enough to reuse it. It appears (as suggested by Hillf Danton) that the search through the RB tree under a read_seqbegin_or_lock() under RCU conditions isn't safe and that it's not blocking the write_seqlock(), despite taking two passes at it. He suggested that the code should take a ref on the cell it's attempting to look at - but this shouldn't be necessary until we've compared the cell names. It's possible that I'm missing a barrier somewhere. However, using an RCU search for this is overkill, really - we only need to access the cell name in a few places, and they're places where we're may end up sleeping anyway. Fix this by switching to an R/W semaphore instead. Additionally, draw the down_read() call inside the function (renamed to afs_find_cell()) since all the callers were taking the RCU read lock (or should've been[*]). [*] afs_probe_cell_name() should have been, but that doesn't appear to be involved in the bug reports. The symptoms of this look like: general protection fault, probably for non-canonical address 0xf27d208691691fdb: 0000 [#1] PREEMPT SMP KASAN KASAN: maybe wild-memory-access in range [0x93e924348b48fed8-0x93e924348b48fedf] ... RIP: 0010:strncasecmp lib/string.c:52 [inline] RIP: 0010:strncasecmp+0x5f/0x240 lib/string.c:43 afs_lookup_cell_rcu+0x313/0x720 fs/afs/cell.c:88 afs_lookup_cell+0x2ee/0x1440 fs/afs/cell.c:249 afs_parse_source fs/afs/super.c:290 [inline] ... Fixes: 989782dcdc91 ("afs: Overhaul cell database management") Reported-by: syzbot+459a5dce0b4cb70fd076@syzkaller.appspotmail.com Signed-off-by: David Howells <dhowells@redhat.com> cc: Hillf Danton <hdanton@sina.com> cc: syzkaller-bugs@googlegroups.com |
| H A D | super.c | diff 92e3cc91 Fri Oct 09 07:11:58 MDT 2020 David Howells <dhowells@redhat.com> afs: Fix rapid cell addition/removal by not using RCU on cells tree There are a number of problems that are being seen by the rapidly mounting and unmounting an afs dynamic root with an explicit cell and volume specified (which should probably be rejected, but that's a separate issue): What the tests are doing is to look up/create a cell record for the name given and then tear it down again without actually using it to try to talk to a server. This is repeated endlessly, very fast, and the new cell collides with the old one if it's not quick enough to reuse it. It appears (as suggested by Hillf Danton) that the search through the RB tree under a read_seqbegin_or_lock() under RCU conditions isn't safe and that it's not blocking the write_seqlock(), despite taking two passes at it. He suggested that the code should take a ref on the cell it's attempting to look at - but this shouldn't be necessary until we've compared the cell names. It's possible that I'm missing a barrier somewhere. However, using an RCU search for this is overkill, really - we only need to access the cell name in a few places, and they're places where we're may end up sleeping anyway. Fix this by switching to an R/W semaphore instead. Additionally, draw the down_read() call inside the function (renamed to afs_find_cell()) since all the callers were taking the RCU read lock (or should've been[*]). [*] afs_probe_cell_name() should have been, but that doesn't appear to be involved in the bug reports. The symptoms of this look like: general protection fault, probably for non-canonical address 0xf27d208691691fdb: 0000 [#1] PREEMPT SMP KASAN KASAN: maybe wild-memory-access in range [0x93e924348b48fed8-0x93e924348b48fedf] ... RIP: 0010:strncasecmp lib/string.c:52 [inline] RIP: 0010:strncasecmp+0x5f/0x240 lib/string.c:43 afs_lookup_cell_rcu+0x313/0x720 fs/afs/cell.c:88 afs_lookup_cell+0x2ee/0x1440 fs/afs/cell.c:249 afs_parse_source fs/afs/super.c:290 [inline] ... Fixes: 989782dcdc91 ("afs: Overhaul cell database management") Reported-by: syzbot+459a5dce0b4cb70fd076@syzkaller.appspotmail.com Signed-off-by: David Howells <dhowells@redhat.com> cc: Hillf Danton <hdanton@sina.com> cc: syzkaller-bugs@googlegroups.com diff 92e3cc91 Fri Oct 09 07:11:58 MDT 2020 David Howells <dhowells@redhat.com> afs: Fix rapid cell addition/removal by not using RCU on cells tree There are a number of problems that are being seen by the rapidly mounting and unmounting an afs dynamic root with an explicit cell and volume specified (which should probably be rejected, but that's a separate issue): What the tests are doing is to look up/create a cell record for the name given and then tear it down again without actually using it to try to talk to a server. This is repeated endlessly, very fast, and the new cell collides with the old one if it's not quick enough to reuse it. It appears (as suggested by Hillf Danton) that the search through the RB tree under a read_seqbegin_or_lock() under RCU conditions isn't safe and that it's not blocking the write_seqlock(), despite taking two passes at it. He suggested that the code should take a ref on the cell it's attempting to look at - but this shouldn't be necessary until we've compared the cell names. It's possible that I'm missing a barrier somewhere. However, using an RCU search for this is overkill, really - we only need to access the cell name in a few places, and they're places where we're may end up sleeping anyway. Fix this by switching to an R/W semaphore instead. Additionally, draw the down_read() call inside the function (renamed to afs_find_cell()) since all the callers were taking the RCU read lock (or should've been[*]). [*] afs_probe_cell_name() should have been, but that doesn't appear to be involved in the bug reports. The symptoms of this look like: general protection fault, probably for non-canonical address 0xf27d208691691fdb: 0000 [#1] PREEMPT SMP KASAN KASAN: maybe wild-memory-access in range [0x93e924348b48fed8-0x93e924348b48fedf] ... RIP: 0010:strncasecmp lib/string.c:52 [inline] RIP: 0010:strncasecmp+0x5f/0x240 lib/string.c:43 afs_lookup_cell_rcu+0x313/0x720 fs/afs/cell.c:88 afs_lookup_cell+0x2ee/0x1440 fs/afs/cell.c:249 afs_parse_source fs/afs/super.c:290 [inline] ... Fixes: 989782dcdc91 ("afs: Overhaul cell database management") Reported-by: syzbot+459a5dce0b4cb70fd076@syzkaller.appspotmail.com Signed-off-by: David Howells <dhowells@redhat.com> cc: Hillf Danton <hdanton@sina.com> cc: syzkaller-bugs@googlegroups.com |
| H A D | internal.h | diff 92e3cc91 Fri Oct 09 07:11:58 MDT 2020 David Howells <dhowells@redhat.com> afs: Fix rapid cell addition/removal by not using RCU on cells tree There are a number of problems that are being seen by the rapidly mounting and unmounting an afs dynamic root with an explicit cell and volume specified (which should probably be rejected, but that's a separate issue): What the tests are doing is to look up/create a cell record for the name given and then tear it down again without actually using it to try to talk to a server. This is repeated endlessly, very fast, and the new cell collides with the old one if it's not quick enough to reuse it. It appears (as suggested by Hillf Danton) that the search through the RB tree under a read_seqbegin_or_lock() under RCU conditions isn't safe and that it's not blocking the write_seqlock(), despite taking two passes at it. He suggested that the code should take a ref on the cell it's attempting to look at - but this shouldn't be necessary until we've compared the cell names. It's possible that I'm missing a barrier somewhere. However, using an RCU search for this is overkill, really - we only need to access the cell name in a few places, and they're places where we're may end up sleeping anyway. Fix this by switching to an R/W semaphore instead. Additionally, draw the down_read() call inside the function (renamed to afs_find_cell()) since all the callers were taking the RCU read lock (or should've been[*]). [*] afs_probe_cell_name() should have been, but that doesn't appear to be involved in the bug reports. The symptoms of this look like: general protection fault, probably for non-canonical address 0xf27d208691691fdb: 0000 [#1] PREEMPT SMP KASAN KASAN: maybe wild-memory-access in range [0x93e924348b48fed8-0x93e924348b48fedf] ... RIP: 0010:strncasecmp lib/string.c:52 [inline] RIP: 0010:strncasecmp+0x5f/0x240 lib/string.c:43 afs_lookup_cell_rcu+0x313/0x720 fs/afs/cell.c:88 afs_lookup_cell+0x2ee/0x1440 fs/afs/cell.c:249 afs_parse_source fs/afs/super.c:290 [inline] ... Fixes: 989782dcdc91 ("afs: Overhaul cell database management") Reported-by: syzbot+459a5dce0b4cb70fd076@syzkaller.appspotmail.com Signed-off-by: David Howells <dhowells@redhat.com> cc: Hillf Danton <hdanton@sina.com> cc: syzkaller-bugs@googlegroups.com diff 92e3cc91 Fri Oct 09 07:11:58 MDT 2020 David Howells <dhowells@redhat.com> afs: Fix rapid cell addition/removal by not using RCU on cells tree There are a number of problems that are being seen by the rapidly mounting and unmounting an afs dynamic root with an explicit cell and volume specified (which should probably be rejected, but that's a separate issue): What the tests are doing is to look up/create a cell record for the name given and then tear it down again without actually using it to try to talk to a server. This is repeated endlessly, very fast, and the new cell collides with the old one if it's not quick enough to reuse it. It appears (as suggested by Hillf Danton) that the search through the RB tree under a read_seqbegin_or_lock() under RCU conditions isn't safe and that it's not blocking the write_seqlock(), despite taking two passes at it. He suggested that the code should take a ref on the cell it's attempting to look at - but this shouldn't be necessary until we've compared the cell names. It's possible that I'm missing a barrier somewhere. However, using an RCU search for this is overkill, really - we only need to access the cell name in a few places, and they're places where we're may end up sleeping anyway. Fix this by switching to an R/W semaphore instead. Additionally, draw the down_read() call inside the function (renamed to afs_find_cell()) since all the callers were taking the RCU read lock (or should've been[*]). [*] afs_probe_cell_name() should have been, but that doesn't appear to be involved in the bug reports. The symptoms of this look like: general protection fault, probably for non-canonical address 0xf27d208691691fdb: 0000 [#1] PREEMPT SMP KASAN KASAN: maybe wild-memory-access in range [0x93e924348b48fed8-0x93e924348b48fedf] ... RIP: 0010:strncasecmp lib/string.c:52 [inline] RIP: 0010:strncasecmp+0x5f/0x240 lib/string.c:43 afs_lookup_cell_rcu+0x313/0x720 fs/afs/cell.c:88 afs_lookup_cell+0x2ee/0x1440 fs/afs/cell.c:249 afs_parse_source fs/afs/super.c:290 [inline] ... Fixes: 989782dcdc91 ("afs: Overhaul cell database management") Reported-by: syzbot+459a5dce0b4cb70fd076@syzkaller.appspotmail.com Signed-off-by: David Howells <dhowells@redhat.com> cc: Hillf Danton <hdanton@sina.com> cc: syzkaller-bugs@googlegroups.com |
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