mm/swap: consider max pages in iomap_swapfile_add_extent

When the max pages (last_page in the swap header + 1) is smaller than
the total pages (inode size) of the swapfile, iomap_swapfile_activate
overwrites sis->max with total pages.

However, frontswap_map is a swap page state bitmap allocated using the
initial sis->max page count read from the swap header. If swapfile
activation increases sis->max, it's possible for the frontswap code to
walk off the end of the bitmap, thereby corrupting kernel memory.

[djwong: modify the description a bit; the original paragraph reads:

"However, frontswap_map is allocated using max pages. When test and clear
the sis offset, which is larger than max pages, of frontswap_map in
__frontswap_invalidate_page(), neighbors of frontswap_map may be
overwritten, i.e., slab is polluted."

Note also that this bug resulted in a behavioral change: activating a
swap file that was formatted and later extended results in all pages
being activated, not the number of pages recorded in the swap header.]

This fixes the issue by considering the limitation of max pages of swap
info in iomap_swapfile_add_extent().

To reproduce the case, compile kernel with slub RED ZONE, then run test:
$ sudo stress-ng -a 1 -x softlockup,resources -t 72h --metrics --times \
--verify -v -Y /root/tmpdir/stress-ng/stress-statistic-12.yaml \
--log-file /root/tmpdir/stress-ng/stress-logfile-12.txt \
--temp-path /root/tmpdir/stress-ng/

We'll get the error log as below:

[ 1151.015141] =============================================================================
[ 1151.016489] BUG kmalloc-16 (Not tainted): Right Redzone overwritten
[ 1151.017486] -----------------------------------------------------------------------------
[ 1151.017486]
[ 1151.018997] Disabling lock debugging due to kernel taint
[ 1151.019873] INFO: 0x0000000084e43932-0x0000000098d17cae @offset=7392. First byte 0x0 instead of 0xcc
[ 1151.021303] INFO: Allocated in __do_sys_swapon+0xcf6/0x1170 age=43417 cpu=9 pid=3816
[ 1151.022538] __slab_alloc+0xe/0x20
[ 1151.023069] __kmalloc_node+0xfd/0x4b0
[ 1151.023704] __do_sys_swapon+0xcf6/0x1170
[ 1151.024346] do_syscall_64+0x33/0x40
[ 1151.024925] entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 1151.025749] INFO: Freed in put_cred_rcu+0xa1/0xc0 age=43424 cpu=3 pid=2041
[ 1151.026889] kfree+0x276/0x2b0
[ 1151.027405] put_cred_rcu+0xa1/0xc0
[ 1151.027949] rcu_do_batch+0x17d/0x410
[ 1151.028566] rcu_core+0x14e/0x2b0
[ 1151.029084] __do_softirq+0x101/0x29e
[ 1151.029645] asm_call_irq_on_stack+0x12/0x20
[ 1151.030381] do_softirq_own_stack+0x37/0x40
[ 1151.031037] do_softirq.part.15+0x2b/0x30
[ 1151.031710] __local_bh_enable_ip+0x4b/0x50
[ 1151.032412] copy_fpstate_to_sigframe+0x111/0x360
[ 1151.033197] __setup_rt_frame+0xce/0x480
[ 1151.033809] arch_do_signal+0x1a3/0x250
[ 1151.034463] exit_to_user_mode_prepare+0xcf/0x110
[ 1151.035242] syscall_exit_to_user_mode+0x27/0x190
[ 1151.035970] entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 1151.036795] INFO: Slab 0x000000003b9de4dc objects=44 used=9 fp=0x00000000539e349e flags=0xfffffc0010201
[ 1151.038323] INFO: Object 0x000000004855ba01 @offset=7376 fp=0x0000000000000000
[ 1151.038323]
[ 1151.039683] Redzone 000000008d0afd3d: cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc ................
[ 1151.041180] Object 000000004855ba01: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
[ 1151.042714] Redzone 0000000084e43932: 00 00 00 c0 cc cc cc cc ........
[ 1151.044120] Padding 000000000864c042: 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a ZZZZZZZZZZZZZZZZ
[ 1151.045615] CPU: 5 PID: 3816 Comm: stress-ng Tainted: G B 5.10.50+ #7
[ 1151.046846] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.1-0-ga5cab58e9a3f-prebuilt.qemu.org 04/01/2014
[ 1151.048633] Call Trace:
[ 1151.049072] dump_stack+0x57/0x6a
[ 1151.049585] check_bytes_and_report+0xed/0x110
[ 1151.050320] check_object+0x1eb/0x290
[ 1151.050924] ? __x64_sys_swapoff+0x39a/0x540
[ 1151.051646] free_debug_processing+0x151/0x350
[ 1151.052333] __slab_free+0x21a/0x3a0
[ 1151.052938] ? _cond_resched+0x2d/0x40
[ 1151.053529] ? __vunmap+0x1de/0x220
[ 1151.054139] ? __x64_sys_swapoff+0x39a/0x540
[ 1151.054796] ? kfree+0x276/0x2b0
[ 1151.055307] kfree+0x276/0x2b0
[ 1151.055832] __x64_sys_swapoff+0x39a/0x540
[ 1151.056466] do_syscall_64+0x33/0x40
[ 1151.057084] entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 1151.057866] RIP: 0033:0x150340b0ffb7
[ 1151.058481] Code: Unable to access opcode bytes at RIP 0x150340b0ff8d.
[ 1151.059537] RSP: 002b:00007fff7f4ee238 EFLAGS: 00000246 ORIG_RAX: 00000000000000a8
[ 1151.060768] RAX: ffffffffffffffda RBX: 00007fff7f4ee66c RCX: 0000150340b0ffb7
[ 1151.061904] RDX: 000000000000000a RSI: 0000000000018094 RDI: 00007fff7f4ee860
[ 1151.063033] RBP: 00007fff7f4ef980 R08: 0000000000000000 R09: 0000150340a672bd
[ 1151.064135] R10: 00007fff7f4edca0 R11: 0000000000000246 R12: 0000000000018094
[ 1151.065253] R13: 0000000000000005 R14: 000000000160d930 R15: 00007fff7f4ee66c
[ 1151.066413] FIX kmalloc-16: Restoring 0x0000000084e43932-0x0000000098d17cae=0xcc
[ 1151.066413]
[ 1151.067890] FIX kmalloc-16: Object at 0x000000004855ba01 not freed

Fixes: 67482129cdab ("iomap: add a swapfile activation function")
Fixes: a45c0eccc564 ("iomap: move the swapfile code into a separate file")
Signed-off-by: Gang Deng <gavin.dg@linux.alibaba.com>
Signed-off-by: Xu Yu <xuyu@linux.alibaba.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>

iomap: switch iomap_swapfile_activate to use iomap_iter

Switch iomap_swapfile_activate to use iomap_iter.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>

iomap: improve the warnings from iomap_swapfile_activate

Print the path name of the swapfile that failed to active to ease
debugging the problem and to avoid a scare if xfstests hits these
cases. Also reword one warning a bit, as the error is not about
a file being on multiple devices, but one that has at least an
extent outside the main device known to the VFS and swap code.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>

iomap: Fix negative assignment to unsigned sis->pages in iomap_swapfile_activate

In case if isi.nr_pages is 0, we are making sis->pages (which is
unsigned int) a huge value in iomap_swapfile_activate() by assigning -1.
This could cause a kernel crash in kernel v4.18 (with below signature).
Or could lead to unknown issues on latest kernel if the fake big swap gets
used.

Fix this issue by returning -EINVAL in case of nr_pages is 0, since it
is anyway a invalid swapfile. Looks like this issue will be hit when
we have pagesize < blocksize type of configuration.

I was able to hit the issue in case of a tiny swap file with below
test script.
https://raw.githubusercontent.com/riteshharjani/LinuxStudy/master/scripts/swap-issue.sh

kernel crash analysis on v4.18
==============================
On v4.18 kernel, it causes a kernel panic, since sis->pages becomes
a huge value and isi.nr_extents is 0. When 0 is returned it is
considered as a swapfile over NFS and SWP_FILE is set (sis->flags |= SWP_FILE).
Then when swapoff was getting called it was calling a_ops->swap_deactivate()
if (sis->flags & SWP_FILE) is true. Since a_ops->swap_deactivate() is
NULL in case of XFS, it causes below panic.

Panic signature on v4.18 kernel:
=======================================
root@qemu:/home/qemu# [ 8291.723351] XFS (loop2): Unmounting Filesystem
[ 8292.123104] XFS (loop2): Mounting V5 Filesystem
[ 8292.132451] XFS (loop2): Ending clean mount
[ 8292.263362] Adding 4294967232k swap on /mnt1/test/swapfile. Priority:-2 extents:1 across:274877906880k
[ 8292.277834] Unable to handle kernel paging request for instruction fetch
[ 8292.278677] Faulting instruction address: 0x00000000
cpu 0x19: Vector: 400 (Instruction Access) at [c0000009dd5b7ad0]
pc: 0000000000000000
lr: c0000000003eb9dc: destroy_swap_extents+0xfc/0x120
sp: c0000009dd5b7d50
msr: 8000000040009033
current = 0xc0000009b6710080
paca = 0xc00000003ffcb280 irqmask: 0x03 irq_happened: 0x01
pid = 5604, comm = swapoff
Linux version 4.18.0 (riteshh@xxxxxxx) (gcc version 8.4.0 (Ubuntu 8.4.0-1ubuntu1~18.04)) #57 SMP Wed Mar 3 01:33:04 CST 2021
enter ? for help
[link register ] c0000000003eb9dc destroy_swap_extents+0xfc/0x120
[c0000009dd5b7d50] c0000000025a7058 proc_poll_event+0x0/0x4 (unreliable)
[c0000009dd5b7da0] c0000000003f0498 sys_swapoff+0x3f8/0x910
[c0000009dd5b7e30] c00000000000bbe4 system_call+0x5c/0x70
Exception: c01 (System Call) at 00007ffff7d208d8

Signed-off-by: Ritesh Harjani <riteshh@linux.ibm.com>
[djwong: rework the comment to provide more details]
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>

iomap: use a srcmap for a read-modify-write I/O

The srcmap is used to identify where the read is to be performed from.
It is passed to ->iomap_begin, which can fill it in if we need to read
data for partially written blocks from a different location than the
write target. The srcmap is only supported for buffered writes so far.

Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
[hch: merged two patches, removed the IOMAP_F_COW flag, use iomap as
srcmap if not set, adjust length down to srcmap end as well]
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Acked-by: Goldwyn Rodrigues <rgoldwyn@suse.com>

iomap: move internal declarations into fs/iomap/

Move internal function declarations out of fs/internal.h into
include/linux/iomap.h so that our transition is complete.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

iomap: move the swapfile code into a separate file

Move the swapfile activation code into a separate file so that we can
group related functions in a single file instead of having a single
enormous source file.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>