Hello,
First, thank you for maintaining the stable branches!
When testing our MPTCP out-of-tree kernel[1] with KASAN last week-end, we saw some new warnings, always the same trace and looking like that:
[ 16.464577] ================================================================== [ 16.465448] BUG: KASAN: slab-out-of-bounds in strscpy+0x49d/0x590 [ 16.466171] Read of size 8 at addr ffff88803525f788 by task confd/330 [ 16.467114] [ 16.467313] CPU: 0 PID: 330 Comm: confd Not tainted 4.14.133-mptcp+ #2 [ 16.468071] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 0.5.1 01/01/2011 [ 16.469016] Call Trace: [ 16.469318] dump_stack+0xa6/0x12e [ 16.469721] ? _atomic_dec_and_lock+0x1b2/0x1b2 [ 16.470255] ? radix_tree_lookup+0x10/0x10 [ 16.470764] ? strscpy+0x49d/0x590 [ 16.471299] print_address_description+0xa1/0x330 [ 16.471918] ? strscpy+0x49d/0x590 [ 16.472321] kasan_report+0x23f/0x350 [ 16.472751] strscpy+0x49d/0x590 [ 16.473135] ? strncpy+0xd0/0xd0 [ 16.473518] p9dirent_read+0x26b/0x510 [ 16.473977] ? unwind_next_frame+0xc97/0x1eb0 [ 16.474481] ? p9stat_read+0x440/0x440 [ 16.474945] ? entry_SYSCALL_64_after_hwframe+0x3d/0xa2 [ 16.475543] ? rcutorture_record_progress+0x10/0x10 [ 16.476123] ? kernel_text_address+0x111/0x120 [ 16.476656] ? __kernel_text_address+0xe/0x30 [ 16.477273] v9fs_dir_readdir_dotl+0x340/0x5b0 [ 16.477900] ? kasan_slab_free+0x12d/0x1a0 [ 16.478377] ? v9fs_dir_readdir+0x810/0x810 [ 16.478887] ? new_slab+0x29f/0x3b0 [ 16.479298] ? iterate_fd+0x300/0x300 [ 16.479728] ? do_filp_open+0x24a/0x3b0 [ 16.480177] ? SyS_getcwd+0x3b7/0x9f0 [ 16.480626] ? may_open_dev+0xc0/0xc0 [ 16.481056] ? get_unused_fd_flags+0x180/0x180 [ 16.481643] ? __up.isra.0+0x230/0x230 [ 16.482195] ? __fdget_pos+0x105/0x170 [ 16.482658] ? iterate_dir+0x171/0x5b0 [ 16.483097] iterate_dir+0x171/0x5b0 [ 16.483518] SyS_getdents+0x1dc/0x3a0 [ 16.483968] ? SyS_old_readdir+0x200/0x200 [ 16.484444] ? SyS_write+0x1c0/0x270 [ 16.484875] ? fillonedir+0x1a0/0x1a0 [ 16.485315] ? SyS_old_readdir+0x200/0x200 [ 16.485791] ? do_syscall_64+0x259/0xa90 [ 16.486258] do_syscall_64+0x259/0xa90 [ 16.486715] ? syscall_return_slowpath+0x340/0x340 [ 16.487320] ? do_page_fault+0x11f/0x400 [ 16.487849] ? __do_page_fault+0xe00/0xe00 [ 16.488305] ? __hrtick_start+0x2f0/0x2f0 [ 16.488752] ? __switch_to_asm+0x31/0x60 [ 16.489189] ? __switch_to_asm+0x31/0x60 [ 16.489626] ? __switch_to_asm+0x25/0x60 [ 16.490063] ? __switch_to_asm+0x31/0x60 [ 16.490500] ? __switch_to_asm+0x31/0x60 [ 16.490940] ? __switch_to_asm+0x31/0x60 [ 16.491377] ? __switch_to_asm+0x25/0x60 [ 16.491820] ? __switch_to_asm+0x31/0x60 [ 16.492305] ? __switch_to_asm+0x31/0x60 [ 16.492769] ? __switch_to_asm+0x31/0x60 [ 16.493306] ? __switch_to_asm+0x31/0x60 [ 16.493917] ? __switch_to_asm+0x31/0x60 [ 16.494402] ? __switch_to_asm+0x25/0x60 [ 16.494859] ? __switch_to_asm+0x31/0x60 [ 16.495344] ? __switch_to_asm+0x31/0x60 [ 16.495798] ? __switch_to_asm+0x31/0x60 [ 16.496283] entry_SYSCALL_64_after_hwframe+0x3d/0xa2 [ 16.496885] RIP: 0033:0x7f0bd5b26855 [ 16.497313] RSP: 002b:00007f0bd69d4d60 EFLAGS: 00000246 ORIG_RAX: 000000000000004e [ 16.498387] RAX: ffffffffffffffda RBX: 00007f0bb800a910 RCX: 00007f0bd5b26855 [ 16.499221] RDX: 0000000000008000 RSI: 00007f0bb800a910 RDI: 000000000000002c [ 16.500102] RBP: 00007f0bb800a910 R08: 00007f0bd69d4e10 R09: 0000000000008030 [ 16.500942] R10: 0000000000000076 R11: 0000000000000246 R12: ffffffffffffff70 [ 16.501780] R13: 0000000000000002 R14: 00007f0bb80008d0 R15: 000000000129cb44 [ 16.502641] [ 16.502819] Allocated by task 330: [ 16.503230] kasan_kmalloc+0xe4/0x170 [ 16.503799] __kmalloc+0xdd/0x1c0 [ 16.504259] p9pdu_readf+0xbb8/0x2940 [ 16.504707] p9dirent_read+0x174/0x510 [ 16.505154] v9fs_dir_readdir_dotl+0x340/0x5b0 [ 16.505694] iterate_dir+0x171/0x5b0 [ 16.506122] SyS_getdents+0x1dc/0x3a0 [ 16.506573] do_syscall_64+0x259/0xa90 [ 16.507031] entry_SYSCALL_64_after_hwframe+0x3d/0xa2 [ 16.507633] [ 16.507804] Freed by task 322: [ 16.508178] kasan_slab_free+0xac/0x1a0 [ 16.508741] kfree+0xcd/0x1e0 [ 16.509194] p9stat_free+0x32/0x200 [ 16.509633] v9fs_vfs_get_link+0x173/0x230 [ 16.510118] ovl_get_link+0x52/0x80 [ 16.510538] trailing_symlink+0x42c/0x5f0 [ 16.511034] path_lookupat+0x1b4/0xc30 [ 16.511481] filename_lookup+0x237/0x470 [ 16.511955] vfs_statx+0xb0/0x120 [ 16.512358] SyS_newstat+0x70/0xc0 [ 16.512759] do_syscall_64+0x259/0xa90 [ 16.513205] entry_SYSCALL_64_after_hwframe+0x3d/0xa2 [ 16.513807] [ 16.514041] The buggy address belongs to the object at ffff88803525f780 [ 16.514041] which belongs to the cache kmalloc-16 of size 16 [ 16.515645] The buggy address is located 8 bytes inside of [ 16.515645] 16-byte region [ffff88803525f780, ffff88803525f790) [ 16.516997] The buggy address belongs to the page: [ 16.517563] page:ffff88803f5407c0 count:1 mapcount:0 mapping: (null) index:0x0 [ 16.518504] flags: 0xc80000000100(slab) [ 16.519103] raw: 0000c80000000100 0000000000000000 0000000000000000 0000000180800080 [ 16.520066] raw: ffff88803f4fa900 0000000800000008 ffff888035c01b40 0000000000000000 [ 16.520981] page dumped because: kasan: bad access detected [ 16.521647] [ 16.521818] Memory state around the buggy address: [ 16.522413] ffff88803525f680: fb fb fc fc fb fb fc fc fb fb fc fc fb fb fc fc [ 16.523258] ffff88803525f700: fb fb fc fc fb fb fc fc fb fb fc fc fb fb fc fc [ 16.524118] >ffff88803525f780: 00 02 fc fc fb fb fc fc fb fb fc fc fb fb fc fc [ 16.525093] ^ [ 16.525591] ffff88803525f800: fb fb fc fc fb fb fc fc fb fb fc fc fb fb fc fc [ 16.526471] ffff88803525f880: fb fb fc fc fb fb fc fc fb fb fc fc fb fb fc fc [ 16.527323] ==================================================================
We are running tests in different KVMs and using 9P for the root RO partition and others for a shared file system between VMs and the host:
mount -t 9p outshare "${MOUNT_DIR}/overlay/out" -o trans=virtio,version=9p2000.L,access=0,rw
Our out-of-tree kernel does not modify the FS part, nor net/9p.
With Dominique from v9fs project, we analysed the issue[2]. At the end, it is confirmed that this KASAN warning is not related to our MPTCP modifications but due to a recent change in the v4.14 stable branch: 84693d060965 (9p: p9dirent_read: check network-provided name length).
In this change backported by Sasha, strcpy() has been replaced by strscpy(). This is known to cause KASAN false-positives, see: 1a3241ff10d0 (lib/strscpy: Shut up KASAN false-positives in strscpy()). Note that this commit depends on the two parent ones.
Could it then be possible to also backport these three commits please?
The three commits apply without any issues. I followed the documention to propose these three commits to stable, the Option 3. Just for me for next time: is it easier for you to propose the patches like I did or to only mention the SHA from Linus GIT tree?
- 1a3241ff10d0 (lib/strscpy: Shut up KASAN false-positives in strscpy()) - 7f1e541fc8d5 (compiler.h: Add read_word_at_a_time() function.) - bdb5ac801af3 (compiler.h, kasan: Avoid duplicating __read_once_size_nocheck())
Cheers, Matt
[1] https://github.com/multipath-tcp/mptcp/ [2] https://sourceforge.net/p/v9fs/mailman/message/36718122/
Andrey Ryabinin (3): compiler.h, kasan: Avoid duplicating __read_once_size_nocheck() compiler.h: Add read_word_at_a_time() function. lib/strscpy: Shut up KASAN false-positives in strscpy()
include/linux/compiler.h | 22 ++++++++++++++-------- lib/string.c | 2 +- 2 files changed, 15 insertions(+), 9 deletions(-)
Cc: Dominique Martinet asmadeus@codewreck.org Cc: Sasha Levin sashal@kernel.org