https://syzkaller.appspot.com/bug?extid=d98fd19acd08b36ff422
[PATCH v3 1/2] bfs: prevent null pointer dereference in bfs_move_block() v3: Changed the error handling
[PATCH v3 2/2] bfs: ensure buffer is marked uptodate before marking it dirty v3: Replaced the buffer up-to-date check with an error exit by forcefully setting the buffer as up-to-date before call mark_buffer_dirty()
From: Vasiliy Kovalev kovalev@altlinux.org
Detect a failed sb_getblk() call (before copying data) so that null pointer dereferences should not happen any more. We also decrement (brelse) the bh counter in this case.
Found when launching the reproducer generated by Syzkaller:
KASAN: null-ptr-deref in range [0x0000000000000028-0x000000000000002f] Comm: mark_buffer_dir Tainted: G W 6.1.105-un-def-alt1.kasan #1 RIP: 0010:bfs_get_block+0x35b/0xdf0 (fs/bfs/file.c:42) [bfs] Call Trace: <TASK> __die_body.cold (arch/x86/kernel/dumpstack.c:478) die_addr (arch/x86/kernel/dumpstack.c:462) exc_general_protection (arch/x86/kernel/traps.c:787) asm_exc_general_protection (./arch/x86/include/asm/idtentry.h:564) __getblk_gfp (fs/buffer.c:1335) bfs_get_block (fs/bfs/file.c:42) bfs bfs_get_block (fs/bfs/file.c:56) bfs bfs_get_block (fs/bfs/file.c:125) bfs bfs_write_begin (fs/bfs/file.c:66) bfs __block_write_begin_int (fs/buffer.c:1991) bfs_write_begin (fs/bfs/file.c:66) bfs invalidate_bh_lrus_cpu (fs/buffer.c:1955) fault_in_readable (mm/gup.c:1898) PageHeadHuge (mm/hugetlb.c:2123) bfs_write_begin (fs/bfs/file.c:66) bfs block_write_begin (fs/buffer.c:2103) bfs_write_begin (fs/bfs/file.c:178) bfs generic_perform_write (mm/filemap.c:3817) generic_file_readonly_mmap (mm/filemap.c:3781) new_inode (fs/inode.c:2126) generic_write_checks (fs/read_write.c:1687) __generic_file_write_iter (mm/filemap.c:3946) generic_file_write_iter (./include/linux/fs.h:763 mm/filemap.c:3978) vfs_write (./include/linux/fs.h:2265 fs/read_write.c:491) kernel_write (fs/read_write.c:565) __fget_files (fs/file.c:918) ksys_write (fs/read_write.c:638)
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Reported-by: syzbot+d98fd19acd08b36ff422@syzkaller.appspotmail.com Link: https://syzkaller.appspot.com/bug?extid=d98fd19acd08b36ff422 Link: https://syzkaller.appspot.com/text?tag=ReproC&x=16515ba3e80000 Cc: stable@vger.kernel.org Signed-off-by: Vasiliy Kovalev kovalev@altlinux.org --- fs/bfs/file.c | 4 ++++ 1 file changed, 4 insertions(+)
diff --git a/fs/bfs/file.c b/fs/bfs/file.c index 57ae5ee6deec12..23773e62994024 100644 --- a/fs/bfs/file.c +++ b/fs/bfs/file.c @@ -39,6 +39,10 @@ static int bfs_move_block(unsigned long from, unsigned long to, if (!bh) return -EIO; new = sb_getblk(sb, to); + if (!new) { + brelse(bh); + return -EIO; + } memcpy(new->b_data, bh->b_data, bh->b_size); mark_buffer_dirty(new); bforget(bh);
From: Vasiliy Kovalev kovalev@altlinux.org
Add a call to `set_buffer_uptodate(new)` in `bfs_move_block` before marking the buffer as dirty. This change ensures the buffer is correctly flagged as containing valid data after copying, preventing potential data inconsistencies or corruption during writeback.
Found by Syzkaller:
WARNING: CPU: 1 PID: 5055 at fs/buffer.c:1176 mark_buffer_dirty+0x37b/0x3f0 fs/buffer.c:1176 Modules linked in: CPU: 1 PID: 5055 Comm: syz-executor162 Not tainted 6.8.0-rc1-syzkaller-00049-g6098d87eaf31 #0 Hardware name: Google Compute Engine/Google Compute Engine, BIOS Google 11/17/2023 RIP: 0010:mark_buffer_dirty+0x37b/0x3f0 fs/buffer.c:1176 Call Trace:
bfs_move_block fs/bfs/file.c:44 [inline] bfs_move_blocks fs/bfs/file.c:57 [inline] bfs_get_block+0x3e5/0xeb0 fs/bfs/file.c:126 __block_write_begin_int+0x4fb/0x16e0 fs/buffer.c:2103 __block_write_begin fs/buffer.c:2152 [inline] block_write_begin+0xb1/0x490 fs/buffer.c:2211 bfs_write_begin+0x31/0xd0 fs/bfs/file.c:179 generic_perform_write+0x278/0x600 mm/filemap.c:3930 __generic_file_write_iter+0x1f9/0x240 mm/filemap.c:4025 generic_file_write_iter+0xe3/0x350 mm/filemap.c:4051 call_write_iter include/linux/fs.h:2085 [inline] new_sync_write fs/read_write.c:497 [inline] vfs_write+0x6d5/0x1100 fs/read_write.c:590 ksys_write+0x12f/0x250 fs/read_write.c:643 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0xd3/0x250 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x63/0x6b
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Reported-by: syzbot+d98fd19acd08b36ff422@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=d98fd19acd08b36ff422 Cc: stable@vger.kernel.org Signed-off-by: Vasiliy Kovalev kovalev@altlinux.org --- fs/bfs/file.c | 1 + 1 file changed, 1 insertion(+)
diff --git a/fs/bfs/file.c b/fs/bfs/file.c index 23773e62994024..3f0c506584560e 100644 --- a/fs/bfs/file.c +++ b/fs/bfs/file.c @@ -44,6 +44,7 @@ static int bfs_move_block(unsigned long from, unsigned long to, return -EIO; } memcpy(new->b_data, bh->b_data, bh->b_size); + set_buffer_uptodate(new); mark_buffer_dirty(new); bforget(bh); brelse(new);
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