* Re: [syzbot] [raid?] UBSAN: array-index-out-of-bounds in super_90_sync
2026-09-13 13:09 [syzbot] [raid?] UBSAN: array-index-out-of-bounds in super_90_sync syzbot
@ 2026-09-13 17:34 ` syzbot
2026-09-14 3:52 ` Forwarded: [PATCH] md: validate raid_disks against MD_SB_DISKS in super_90_load syzbot
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: syzbot @ 2026-09-13 17:34 UTC (permalink / raw)
To: linux-kernel, linux-raid, magiclinan, song, syzkaller-bugs, xiao,
yukuai, yukuai
syzbot has found a reproducer for the following issue on:
HEAD commit: 2f0c1cf72f46 Merge tag 's390-7.3-3' of git://git.kernel.or..
git tree: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=14afd5f9580000
kernel config: https://syzkaller.appspot.com/x/.config?x=8c5c3949d762a91f
dashboard link: https://syzkaller.appspot.com/bug?extid=9e3014263a35700ab49b
compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=12afd5f9580000
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+9e3014263a35700ab49b@syzkaller.appspotmail.com
------------[ cut here ]------------
UBSAN: array-index-out-of-bounds in drivers/md/md.c:1697:17
index 124 is out of range for type 'mdp_disk_t [27]'
CPU: 1 UID: 0 PID: 6018 Comm: syz-executor186 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
ubsan_epilogue+0xa/0x30 lib/ubsan.c:233
__ubsan_handle_out_of_bounds+0xcc/0xf0 lib/ubsan.c:455
super_90_sync+0x1eed/0x1ff0 drivers/md/md.c:1697
sync_super drivers/md/md.c:2505 [inline]
sync_sbs drivers/md/md.c:2747 [inline]
md_update_sb+0xbba/0x2840 drivers/md/md.c:2923
state_store+0x31e/0x1340 drivers/md/md.c:3245
rdev_attr_store+0x1d9/0x560 drivers/md/md.c:3768
sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:145
kernfs_fop_write_iter+0x3e0/0x5f0 fs/kernfs/file.c:345
new_sync_write fs/read_write.c:595 [inline]
vfs_write+0x6af/0x1050 fs/read_write.c:687
ksys_write+0x12a/0x250 fs/read_write.c:739
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f84634ad6f7
Code: 48 89 fa 4c 89 df e8 98 1d 00 00 8b 93 08 03 00 00 59 5e 48 83 f8 fc 74 1a 5b c3 0f 1f 84 00 00 00 00 00 48 8b 44 24 10 0f 05 <5b> c3 0f 1f 80 00 00 00 00 83 e2 39 83 fa 08 75 de e8 23 ff ff ff
RSP: 002b:00007fff04c70ef0 EFLAGS: 00000202 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00005555934c5400 RCX: 00007f84634ad6f7
RDX: 0000000000000008 RSI: 00007f84634e9c12 RDI: 0000000000000003
RBP: 00007f84634e9c12 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 00007fff04c70fc0
R13: 00007f84634e9b5f R14: 00007fff04c710d0 R15: 0000000000000002
</TASK>
---[ end trace ]---
---
If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.
^ permalink raw reply [flat|nested] 5+ messages in thread* Forwarded: [PATCH] md: validate raid_disks against MD_SB_DISKS in super_90_load
2026-09-13 13:09 [syzbot] [raid?] UBSAN: array-index-out-of-bounds in super_90_sync syzbot
2026-09-13 17:34 ` syzbot
@ 2026-09-14 3:52 ` syzbot
2026-09-14 4:22 ` Forwarded: [PATCH] md: fix out-of-bounds access to superblock disk array syzbot
2026-09-14 7:44 ` Forwarded: [PATCH] configfs: unhash dentry before dropping the item syzbot
3 siblings, 0 replies; 5+ messages in thread
From: syzbot @ 2026-09-14 3:52 UTC (permalink / raw)
To: linux-kernel, syzkaller-bugs
For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com.
***
Subject: [PATCH] md: validate raid_disks against MD_SB_DISKS in super_90_load
Author: kartikey406@gmail.com
#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
The v0.90 superblock format can only describe MD_SB_DISKS (27) member
disks, but super_90_load() only checks that sb->raid_disks is
positive, not that it fits within this limit.
A crafted/corrupt superblock with an oversized raid_disks value is
accepted and copied into mddev->raid_disks. When the superblock is
later rewritten (e.g. via a write to the rdev 'state' sysfs
attribute), super_90_sync() uses this value to index sb->disks[],
causing an out-of-bounds array access:
UBSAN: array-index-out-of-bounds in drivers/md/md.c:1697:17
index 124 is out of range for type 'mdp_disk_t [27]'
Reject superblocks whose raid_disks value cannot be represented by
the v0.90 format at load time, before it is trusted anywhere else.
Reported-by: syzbot+9e3014263a35700ab49b@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=9e3014263a35700ab49b
Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
---
drivers/md/md.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/drivers/md/md.c b/drivers/md/md.c
index 680b34a63cb3..c65da77677bc 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -1393,7 +1393,8 @@ static int super_90_load(struct md_rdev *rdev, struct md_rdev *refdev, int minor
goto abort;
}
- if (sb->raid_disks <= 0)
+ if (sb->raid_disks <= 0 ||
+ sb->raid_disks > MD_SB_DISKS)
goto abort;
if (md_csum_fold(calc_sb_csum(sb)) != md_csum_fold(sb->sb_csum)) {
--
2.34.1
^ permalink raw reply [flat|nested] 5+ messages in thread* Forwarded: [PATCH] md: fix out-of-bounds access to superblock disk array
2026-09-13 13:09 [syzbot] [raid?] UBSAN: array-index-out-of-bounds in super_90_sync syzbot
2026-09-13 17:34 ` syzbot
2026-09-14 3:52 ` Forwarded: [PATCH] md: validate raid_disks against MD_SB_DISKS in super_90_load syzbot
@ 2026-09-14 4:22 ` syzbot
2026-09-14 7:44 ` Forwarded: [PATCH] configfs: unhash dentry before dropping the item syzbot
3 siblings, 0 replies; 5+ messages in thread
From: syzbot @ 2026-09-14 4:22 UTC (permalink / raw)
To: linux-kernel, syzkaller-bugs
For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com.
***
Subject: [PATCH] md: fix out-of-bounds access to superblock disk array
Author: kartikey406@gmail.com
#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
The v0.90 superblock format can only describe MD_SB_DISKS (27) member
disks, but several places did not enforce this limit, allowing an
out-of-bounds access to sb->disks[]:
1. super_90_load() only checked that sb->raid_disks was positive,
not that it fit within MD_SB_DISKS. A crafted superblock with an
oversized raid_disks value was accepted into mddev->raid_disks.
2. super_90_sync() computed desc_nr from rdev2->raid_disk or a
running spare counter without checking it stayed within bounds
before indexing sb->disks[desc_nr].
3. super_90_sync() also indexed sb->disks[rdev->desc_nr] for
sb->this_disk without any bounds check.
4. The "missing devices" loop in super_90_sync() iterated up to
mddev->raid_disks with no per-iteration bound on sb->disks[].
Any of these could be reached with a bad raid_disks/desc_nr value
and cause an out-of-bounds array access:
UBSAN: array-index-out-of-bounds in drivers/md/md.c:1697:17
index 124 is out of range for type 'mdp_disk_t [27]'
Validate raid_disks at load time, and add bounds checks at each
point sb->disks[] is indexed as defense in depth.
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reported-by: syzbot+9e3014263a35700ab49b@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=9e3014263a35700ab49b
Assisted-by: Claude
Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
---
drivers/md/md.c | 19 +++++++++++++++----
1 file changed, 15 insertions(+), 4 deletions(-)
diff --git a/drivers/md/md.c b/drivers/md/md.c
index 680b34a63cb3..f950e6fd144c 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -1393,7 +1393,8 @@ static int super_90_load(struct md_rdev *rdev, struct md_rdev *refdev, int minor
goto abort;
}
- if (sb->raid_disks <= 0)
+ if (sb->raid_disks <= 0 ||
+ sb->raid_disks > MD_SB_DISKS)
goto abort;
if (md_csum_fold(calc_sb_csum(sb)) != md_csum_fold(sb->sb_csum)) {
@@ -1693,6 +1694,13 @@ static void super_90_sync(struct mddev *mddev, struct md_rdev *rdev)
desc_nr = rdev2->raid_disk;
else
desc_nr = next_spare++;
+
+ if (desc_nr < 0 || desc_nr >= MD_SB_DISKS) {
+ pr_warn("md: %s: desc_nr %d out of range for rdev %pg, skipping\n",
+ mdname(mddev), desc_nr, rdev2->bdev);
+ continue;
+ }
+
rdev2->desc_nr = desc_nr;
d = &sb->disks[rdev2->desc_nr];
nr_disks++;
@@ -1722,7 +1730,7 @@ static void super_90_sync(struct mddev *mddev, struct md_rdev *rdev)
d->state |= (1<<MD_DISK_FAILFAST);
}
/* now set the "removed" and "faulty" bits on any missing devices */
- for (i=0 ; i < mddev->raid_disks ; i++) {
+ for (i=0 ; i < mddev->raid_disks && i < MD_SB_DISKS ; i++) {
mdp_disk_t *d = &sb->disks[i];
if (d->state == 0 && d->number == 0) {
d->number = i;
@@ -1737,8 +1745,11 @@ static void super_90_sync(struct mddev *mddev, struct md_rdev *rdev)
sb->working_disks = working;
sb->failed_disks = failed;
sb->spare_disks = spare;
-
- sb->this_disk = sb->disks[rdev->desc_nr];
+ if (rdev->desc_nr >= 0 && rdev->desc_nr < MD_SB_DISKS)
+ sb->this_disk = sb->disks[rdev->desc_nr];
+ else
+ pr_warn("md: %s: rdev desc_nr %d out of range, this_disk not set\n",
+ mdname(mddev), rdev->desc_nr);
sb->sb_csum = calc_sb_csum(sb);
}
--
2.34.1
^ permalink raw reply [flat|nested] 5+ messages in thread* Forwarded: [PATCH] configfs: unhash dentry before dropping the item
2026-09-13 13:09 [syzbot] [raid?] UBSAN: array-index-out-of-bounds in super_90_sync syzbot
` (2 preceding siblings ...)
2026-09-14 4:22 ` Forwarded: [PATCH] md: fix out-of-bounds access to superblock disk array syzbot
@ 2026-09-14 7:44 ` syzbot
3 siblings, 0 replies; 5+ messages in thread
From: syzbot @ 2026-09-14 7:44 UTC (permalink / raw)
To: linux-kernel
For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org.
***
Subject: [PATCH] configfs: unhash dentry before dropping the item
Author: jchuang26@m.fudan.edu.cn
#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
Reported-by: syzbot+9e3014263a35700ab49b@syzkaller.appspotmail.com
diff --git a/drivers/md/md.c b/drivers/md/md.c
index 680b34a63..bcc32b83c 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -1393,7 +1393,11 @@ static int super_90_load(struct md_rdev *rdev, struct md_rdev *refdev, int minor
goto abort;
}
- if (sb->raid_disks <= 0)
+ /*
+ * sb->disks[] has only MD_SB_DISKS entries. A larger raid_disks
+ * count would later make super_90_sync() index past that array.
+ */
+ if (sb->raid_disks <= 0 || sb->raid_disks > MD_SB_DISKS)
goto abort;
if (md_csum_fold(calc_sb_csum(sb)) != md_csum_fold(sb->sb_csum)) {
@@ -1607,6 +1611,18 @@ static void super_90_sync(struct mddev *mddev, struct md_rdev *rdev)
struct md_rdev *rdev2;
int next_spare = mddev->raid_disks;
+ /*
+ * A 0.90 superblock has a fixed-size mdp_disk_t array and uses
+ * raid_disks as both a loop bound and the first spare disk slot.
+ * Never index sb->disks[] if an invalid raid_disks value reached
+ * us through any configuration path.
+ */
+ if (mddev->raid_disks < 0 || mddev->raid_disks > MD_SB_DISKS) {
+ pr_warn("md: %s: invalid raid_disks %d for 0.90 metadata\n",
+ mdname(mddev), mddev->raid_disks);
+ return;
+ }
+
/* make rdev->sb match mddev data..
*
* 1/ zero out disks
@@ -4448,8 +4464,19 @@ raid_disks_store(struct mddev *mddev, const char *buf, size_t len)
mddev->delta_disks = n - olddisks;
mddev->raid_disks = n;
mddev->reshape_backwards = (mddev->delta_disks < 0);
- } else
- mddev->raid_disks = n;
+ } else {
+ /*
+ * 0.90 metadata only has room for MD_SB_DISKS descriptors.
+ * Larger values would make super_90_sync() index beyond
+ * sb->disks[].
+ */
+ if ((mddev->persistent && mddev->major_version == 0 &&
+ n > MD_SB_DISKS) ||
+ (mddev->max_disks && n > mddev->max_disks))
+ err = -EINVAL;
+ else
+ mddev->raid_disks = n;
+ }
out_unlock:
memalloc_noio_restore(noio_flags);
mddev_unlock_and_resume(mddev);
@@ -7926,6 +7953,18 @@ int md_set_array_info(struct mddev *mddev, struct mdu_array_info_s *info)
mddev->ctime = ktime_get_real_seconds();
return 0;
}
+
+ /*
+ * Persistent 0.90 metadata stores disks in sb->disks[MD_SB_DISKS].
+ * A larger raid_disks count would make super_90_sync() index past
+ * that array; non-persistent arrays have no such on-disk limit.
+ */
+ if (info->raid_disks < 0 ||
+ (!info->not_persistent && info->raid_disks > MD_SB_DISKS)) {
+ pr_warn("md: invalid raid_disks %d\n", info->raid_disks);
+ return -EINVAL;
+ }
+
mddev->major_version = MD_MAJOR_VERSION;
mddev->minor_version = MD_MINOR_VERSION;
mddev->patch_version = MD_PATCHLEVEL_VERSION;
^ permalink raw reply [flat|nested] 5+ messages in thread