CVE-2024-26658

In the Linux kernel, the following vulnerability has been resolved:
bcachefs: grab s_umount only if snapshotting When I was testing mongodb
over bcachefs with compression, there is a lockdep warning when
snapshotting mongodb data volume. $ cat test.sh prog=bcachefs $prog
subvolume create /mnt/data $prog subvolume create /mnt/data/snapshots while
true;do $prog subvolume snapshot /mnt/data /mnt/data/snapshots/$(date +%s)
sleep 1s done $ cat /etc/mongodb.conf systemLog: destination: file
logAppend: true path: /mnt/data/mongod.log storage: dbPath: /mnt/data/
lockdep reports: [ 3437.452330]
====================================================== [ 3437.452750]
WARNING: possible circular locking dependency detected [ 3437.453168]
6.7.0-rc7-custom+ #85 Tainted: G E [ 3437.453562]
------------------------------------------------------ [ 3437.453981]
bcachefs/35533 is trying to acquire lock: [ 3437.454325] ffffa0a02b2b1418
(sb_writers#10){.+.+}-{0:0}, at: filename_create+0x62/0x190 [ 3437.454875]
but task is already holding lock: [ 3437.455268] ffffa0a02b2b10e0
(&type->s_umount_key#48){.+.+}-{3:3}, at: bch2_fs_file_ioctl+0x232/0xc90
[bcachefs] [ 3437.456009] which lock already depends on the new lock. [
3437.456553] the existing dependency chain (in reverse order) is: [
3437.457054] -> #3 (&type->s_umount_key#48){.+.+}-{3:3}: [ 3437.457507]
down_read+0x3e/0x170 [ 3437.457772] bch2_fs_file_ioctl+0x232/0xc90
[bcachefs] [ 3437.458206] __x64_sys_ioctl+0x93/0xd0 [ 3437.458498]
do_syscall_64+0x42/0xf0 [ 3437.458779]
entry_SYSCALL_64_after_hwframe+0x6e/0x76 [ 3437.459155] -> #2
(&c->snapshot_create_lock){++++}-{3:3}: [ 3437.459615] down_read+0x3e/0x170
[ 3437.459878] bch2_truncate+0x82/0x110 [bcachefs] [ 3437.460276]
bchfs_truncate+0x254/0x3c0 [bcachefs] [ 3437.460686]
notify_change+0x1f1/0x4a0 [ 3437.461283] do_truncate+0x7f/0xd0 [
3437.461555] path_openat+0xa57/0xce0 [ 3437.461836] do_filp_open+0xb4/0x160
[ 3437.462116] do_sys_openat2+0x91/0xc0 [ 3437.462402]
__x64_sys_openat+0x53/0xa0 [ 3437.462701] do_syscall_64+0x42/0xf0 [
3437.462982] entry_SYSCALL_64_after_hwframe+0x6e/0x76 [ 3437.463359] -> #1
(&sb->s_type->i_mutex_key#15){+.+.}-{3:3}: [ 3437.463843]
down_write+0x3b/0xc0 [ 3437.464223] bch2_write_iter+0x5b/0xcc0 [bcachefs] [
3437.464493] vfs_write+0x21b/0x4c0 [ 3437.464653] ksys_write+0x69/0xf0 [
3437.464839] do_syscall_64+0x42/0xf0 [ 3437.465009]
entry_SYSCALL_64_after_hwframe+0x6e/0x76 [ 3437.465231] -> #0
(sb_writers#10){.+.+}-{0:0}: [ 3437.465471] __lock_acquire+0x1455/0x21b0 [
3437.465656] lock_acquire+0xc6/0x2b0 [ 3437.465822]
mnt_want_write+0x46/0x1a0 [ 3437.465996] filename_create+0x62/0x190 [
3437.466175] user_path_create+0x2d/0x50 [ 3437.466352]
bch2_fs_file_ioctl+0x2ec/0xc90 [bcachefs] [ 3437.466617]
__x64_sys_ioctl+0x93/0xd0 [ 3437.466791] do_syscall_64+0x42/0xf0 [
3437.466957] entry_SYSCALL_64_after_hwframe+0x6e/0x76 [ 3437.467180] other
info that might help us debug this: [ 3437.469670] 2 locks held by
bcachefs/35533: other info that might help us debug this: [ 3437.467507]
Chain exists of: sb_writers#10 –> &c->snapshot_create_lock –>
&type->s_umount_key#48 [ 3437.467979] Possible unsafe locking scenario: [
3437.468223] CPU0 CPU1 [ 3437.468405] ---- ---- [ 3437.468585]
rlock(&type->s_umount_key#48); [ 3437.468758]
lock(&c->snapshot_create_lock); [ 3437.469030]
lock(&type->s_umount_key#48); [ 3437.469291] rlock(sb_writers#10); [
3437.469434] *** DEADLOCK*** [ 3437.469 —truncated—