| Message ID | 80137af65712e7c2a8ac301b7b9a3901e8bdb44d.1735792000.git.wqu@suse.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | btrfs: avoid NULL pointer dereference if no valid extent tree | expand |
On 2/1/25 09:57, Qu Wenruo wrote: > [BUG] > Syzbot reported a crash with the following call trace: > > BTRFS info (device loop0): scrub: started on devid 1 > BUG: kernel NULL pointer dereference, address: 0000000000000208 > #PF: supervisor read access in kernel mode > #PF: error_code(0x0000) - not-present page > PGD 106e70067 P4D 106e70067 PUD 107143067 PMD 0 > Oops: Oops: 0000 [#1] PREEMPT SMP NOPTI > CPU: 1 UID: 0 PID: 689 Comm: repro Kdump: loaded Tainted: G O 6.13.0-rc4-custom+ #206 > Tainted: [O]=OOT_MODULE > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS unknown 02/02/2022 > RIP: 0010:find_first_extent_item+0x26/0x1f0 [btrfs] > Call Trace: > <TASK> > scrub_find_fill_first_stripe+0x13d/0x3b0 [btrfs] > scrub_simple_mirror+0x175/0x260 [btrfs] > scrub_stripe+0x5d4/0x6c0 [btrfs] > scrub_chunk+0xbb/0x170 [btrfs] > scrub_enumerate_chunks+0x2f4/0x5f0 [btrfs] > btrfs_scrub_dev+0x240/0x600 [btrfs] > btrfs_ioctl+0x1dc8/0x2fa0 [btrfs] > ? do_sys_openat2+0xa5/0xf0 > __x64_sys_ioctl+0x97/0xc0 > do_syscall_64+0x4f/0x120 > entry_SYSCALL_64_after_hwframe+0x76/0x7e > </TASK> > > [CAUSE] > The reproducer is using a corrupted image where extent tree root is > corrupted, thus forcing to use "rescue=all,ro" mount option to mount the > image. > > Then it triggered a scrub, but since scrub relies on extent tree to find > where the data/metadata extents are, scrub_find_fill_first_stripe() > relies on an non-empty extent root. > > But unfortunately scrub_find_fill_first_stripe() doesn't really expect > an NULL pointer for extent root, it use extent_root to grab fs_info and > triggered a NULL pointer dereference. > > [FIX] > Add an extra check for a valid extent root at the beginning of > scrub_find_fill_first_stripe(). > > The new error path is introduced by 42437a6386ff ("btrfs: introduce > mount option rescue=ignorebadroots"), but that's pretty old, and later > commit b979547513ff ("btrfs: scrub: introduce helper to find and fill > sector info for a scrub_stripe") changed how we do scrub. > > So for kernels older than 6.6, the fix will need manual backport. > > Reported-by: syzbot+339e9dbe3a2ca419b85d@syzkaller.appspotmail.com > Link: https://lore.kernel.org/linux-btrfs/67756935.050a0220.25abdd.0a12.GAE@google.com/ > Fixes: 42437a6386ff ("btrfs: introduce mount option rescue=ignorebadroots") > Signed-off-by: Qu Wenruo <wqu@suse.com> Reviewed-by: Anand Jain <anand.jain@oracle.com> Thx, Anand > --- > fs/btrfs/scrub.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c > index 204c928beaf9..531312efee8d 100644 > --- a/fs/btrfs/scrub.c > +++ b/fs/btrfs/scrub.c > @@ -1541,6 +1541,10 @@ static int scrub_find_fill_first_stripe(struct btrfs_block_group *bg, > u64 extent_gen; > int ret; > > + if (unlikely(!extent_root)) { > + btrfs_err(fs_info, "no valid extent root for scrub"); > + return -EUCLEAN; > + } > memset(stripe->sectors, 0, sizeof(struct scrub_sector_verification) * > stripe->nr_sectors); > scrub_stripe_reset_bitmaps(stripe);
diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c index 204c928beaf9..531312efee8d 100644 --- a/fs/btrfs/scrub.c +++ b/fs/btrfs/scrub.c @@ -1541,6 +1541,10 @@ static int scrub_find_fill_first_stripe(struct btrfs_block_group *bg, u64 extent_gen; int ret; + if (unlikely(!extent_root)) { + btrfs_err(fs_info, "no valid extent root for scrub"); + return -EUCLEAN; + } memset(stripe->sectors, 0, sizeof(struct scrub_sector_verification) * stripe->nr_sectors); scrub_stripe_reset_bitmaps(stripe);
[BUG] Syzbot reported a crash with the following call trace: BTRFS info (device loop0): scrub: started on devid 1 BUG: kernel NULL pointer dereference, address: 0000000000000208 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 106e70067 P4D 106e70067 PUD 107143067 PMD 0 Oops: Oops: 0000 [#1] PREEMPT SMP NOPTI CPU: 1 UID: 0 PID: 689 Comm: repro Kdump: loaded Tainted: G O 6.13.0-rc4-custom+ #206 Tainted: [O]=OOT_MODULE Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS unknown 02/02/2022 RIP: 0010:find_first_extent_item+0x26/0x1f0 [btrfs] Call Trace: <TASK> scrub_find_fill_first_stripe+0x13d/0x3b0 [btrfs] scrub_simple_mirror+0x175/0x260 [btrfs] scrub_stripe+0x5d4/0x6c0 [btrfs] scrub_chunk+0xbb/0x170 [btrfs] scrub_enumerate_chunks+0x2f4/0x5f0 [btrfs] btrfs_scrub_dev+0x240/0x600 [btrfs] btrfs_ioctl+0x1dc8/0x2fa0 [btrfs] ? do_sys_openat2+0xa5/0xf0 __x64_sys_ioctl+0x97/0xc0 do_syscall_64+0x4f/0x120 entry_SYSCALL_64_after_hwframe+0x76/0x7e </TASK> [CAUSE] The reproducer is using a corrupted image where extent tree root is corrupted, thus forcing to use "rescue=all,ro" mount option to mount the image. Then it triggered a scrub, but since scrub relies on extent tree to find where the data/metadata extents are, scrub_find_fill_first_stripe() relies on an non-empty extent root. But unfortunately scrub_find_fill_first_stripe() doesn't really expect an NULL pointer for extent root, it use extent_root to grab fs_info and triggered a NULL pointer dereference. [FIX] Add an extra check for a valid extent root at the beginning of scrub_find_fill_first_stripe(). The new error path is introduced by 42437a6386ff ("btrfs: introduce mount option rescue=ignorebadroots"), but that's pretty old, and later commit b979547513ff ("btrfs: scrub: introduce helper to find and fill sector info for a scrub_stripe") changed how we do scrub. So for kernels older than 6.6, the fix will need manual backport. Reported-by: syzbot+339e9dbe3a2ca419b85d@syzkaller.appspotmail.com Link: https://lore.kernel.org/linux-btrfs/67756935.050a0220.25abdd.0a12.GAE@google.com/ Fixes: 42437a6386ff ("btrfs: introduce mount option rescue=ignorebadroots") Signed-off-by: Qu Wenruo <wqu@suse.com> --- fs/btrfs/scrub.c | 4 ++++ 1 file changed, 4 insertions(+)