* Re: [syzbot] [jfs?] UBSAN: shift-out-of-bounds in dbJoin (2)
2025-12-06 16:31 [syzbot] [jfs?] UBSAN: shift-out-of-bounds in dbJoin (2) syzbot
@ 2025-12-07 3:18 ` Edward Adam Davis
2025-12-07 3:52 ` syzbot
2025-12-07 3:52 ` [PATCH] jfs: Add a sanity check for budmin Edward Adam Davis
` (3 subsequent siblings)
4 siblings, 1 reply; 7+ messages in thread
From: Edward Adam Davis @ 2025-12-07 3:18 UTC (permalink / raw)
To: syzbot+fa603ae6b02658401ca7; +Cc: linux-kernel, syzkaller-bugs
#syz test
diff --git a/fs/jfs/jfs_dmap.c b/fs/jfs/jfs_dmap.c
index cdfa699cd7c8..7c35e69cafb9 100644
--- a/fs/jfs/jfs_dmap.c
+++ b/fs/jfs/jfs_dmap.c
@@ -2291,6 +2291,8 @@ static int dbFreeBits(struct bmap * bmp, struct dmap * dp, s64 blkno,
int rc = 0;
int size;
+ if (tp->dmt_budmin < 0)
+ return -EUCLEAN;
/* determine the bit number and word within the dmap of the
* starting block.
*/
^ permalink raw reply related [flat|nested] 7+ messages in thread* [PATCH] jfs: Add a sanity check for budmin
2025-12-06 16:31 [syzbot] [jfs?] UBSAN: shift-out-of-bounds in dbJoin (2) syzbot
2025-12-07 3:18 ` Edward Adam Davis
@ 2025-12-07 3:52 ` Edward Adam Davis
2026-04-17 10:11 ` Forwarded: [PATCH] jfs: fix shift-out-of-bounds in dbJoin syzbot
` (2 subsequent siblings)
4 siblings, 0 replies; 7+ messages in thread
From: Edward Adam Davis @ 2025-12-07 3:52 UTC (permalink / raw)
To: syzbot+fa603ae6b02658401ca7
Cc: jfs-discussion, linux-kernel, shaggy, syzkaller-bugs
In a corrupted file system image, the budmin value is less than 0,
which causes the lazycommit thread to report an out-of-bounds error
when retrieving the buddy size in dbJoin [1].
Add a check for potentially negative budmin to avoid the problem in [1].
[1]
UBSAN: shift-out-of-bounds in fs/jfs/jfs_dmap.c:2795:11
shift exponent 132 is too large for 32-bit type 'int'
Call Trace:
dbJoin+0x2dc/0x300 fs/jfs/jfs_dmap.c:2795
dbFreeBits+0x4e1/0xdb0 fs/jfs/jfs_dmap.c:2340
dbFreeDmap fs/jfs/jfs_dmap.c:2089 [inline]
dbFree+0x336/0x650 fs/jfs/jfs_dmap.c:398
txFreeMap+0x7ff/0xde0 fs/jfs/jfs_txnmgr.c:2535
txUpdateMap+0x308/0x9c0 fs/jfs/jfs_txnmgr.c:-1
txLazyCommit fs/jfs/jfs_txnmgr.c:2665 [inline]
jfs_lazycommit+0x3f1/0xa10 fs/jfs/jfs_txnmgr.c:2734
Reported-by: syzbot+fa603ae6b02658401ca7@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=fa603ae6b02658401ca7
Tested-by: syzbot+fa603ae6b02658401ca7@syzkaller.appspotmail.com
Signed-off-by: Edward Adam Davis <eadavis@qq.com>
---
fs/jfs/jfs_dmap.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/fs/jfs/jfs_dmap.c b/fs/jfs/jfs_dmap.c
index cdfa699cd7c8..8f8084756e32 100644
--- a/fs/jfs/jfs_dmap.c
+++ b/fs/jfs/jfs_dmap.c
@@ -2291,6 +2291,8 @@ static int dbFreeBits(struct bmap * bmp, struct dmap * dp, s64 blkno,
int rc = 0;
int size;
+ if (tp->dmt_budmin < 0)
+ return -EUCLEAN;
/* determine the bit number and word within the dmap of the
* starting block.
*/
--
2.43.0
^ permalink raw reply related [flat|nested] 7+ messages in thread* Forwarded: [PATCH] jfs: fix shift-out-of-bounds in dbJoin
2025-12-06 16:31 [syzbot] [jfs?] UBSAN: shift-out-of-bounds in dbJoin (2) syzbot
2025-12-07 3:18 ` Edward Adam Davis
2025-12-07 3:52 ` [PATCH] jfs: Add a sanity check for budmin Edward Adam Davis
@ 2026-04-17 10:11 ` syzbot
2026-04-17 16:19 ` Forwarded: Re: [syzbot] UBSAN: " syzbot
2026-04-17 19:19 ` Forwarded: Re: [syzbot] [jfs?] UBSAN: shift-out-of-bounds in dbJoin (2) syzbot
4 siblings, 0 replies; 7+ messages in thread
From: syzbot @ 2026-04-17 10:11 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] jfs: fix shift-out-of-bounds in dbJoin
Author: tristmd@gmail.com
From: Tristan Madani <tristan@talencesecurity.com>
#syz test: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
dbJoin() computes a buddy size via BUDSIZE(newval, budmin), which
expands to 1 << (newval - budmin). If the on-disk tree metadata is
corrupted such that the leaf values or free counts are inconsistent,
newval can exceed budmin + 31, causing a shift-out-of-bounds:
UBSAN: shift-out-of-bounds in fs/jfs/jfs_dmap.c:2882:11
shift exponent 132 is too large for 32-bit type 'int'
The maximum meaningful newval for a given tree is budmin + l2nleafs,
since BUDSIZE at that point equals nleafs and the while loop would not
execute. Any value beyond that indicates corrupted metadata.
Add a sanity check before the BUDSIZE call: if newval exceeds
budmin + l2nleafs, return -EIO.
Reported-by: syzbot+fa603ae6b02658401ca7@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=fa603ae6b02658401ca7
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Signed-off-by: Tristan Madani <tristan@talencesecurity.com>
---
fs/jfs/jfs_dmap.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/fs/jfs/jfs_dmap.c b/fs/jfs/jfs_dmap.c
index XXXXXXX..XXXXXXX 100644
--- a/fs/jfs/jfs_dmap.c
+++ b/fs/jfs/jfs_dmap.c
@@ -2864,6 +2864,14 @@ static int dbJoin(dmtree_t *tp, int leafno, int newval, bool is_ctl)
if (newval >= tp->dmt_budmin) {
/* pickup a pointer to the leaves of the tree.
*/
+
+ /* Validate newval to prevent shift-out-of-bounds in
+ * BUDSIZE. The maximum meaningful value is budmin +
+ * l2nleafs; anything beyond indicates corrupted metadata.
+ */
+ if (newval > tp->dmt_budmin +
+ le32_to_cpu(tp->dmt_l2nleafs))
+ return -EIO;
leaf = tp->dmt_stree + le32_to_cpu(tp->dmt_leafidx);
/* try to join the specified leaf into a large binary
--
2.39.5
^ permalink raw reply [flat|nested] 7+ messages in thread* Forwarded: Re: [syzbot] UBSAN: shift-out-of-bounds in dbJoin
2025-12-06 16:31 [syzbot] [jfs?] UBSAN: shift-out-of-bounds in dbJoin (2) syzbot
` (2 preceding siblings ...)
2026-04-17 10:11 ` Forwarded: [PATCH] jfs: fix shift-out-of-bounds in dbJoin syzbot
@ 2026-04-17 16:19 ` syzbot
2026-04-17 19:19 ` Forwarded: Re: [syzbot] [jfs?] UBSAN: shift-out-of-bounds in dbJoin (2) syzbot
4 siblings, 0 replies; 7+ messages in thread
From: syzbot @ 2026-04-17 16:19 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: Re: [syzbot] UBSAN: shift-out-of-bounds in dbJoin
Author: tristmd@gmail.com
#syz test: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
>From b3eba06211261ff42d58377c02b45bf48aae8f82 Mon Sep 17 00:00:00 2001
From: Tristan Madani <tristan@talencesecurity.com>
Date: Fri, 17 Apr 2026 16:15:14 +0000
Subject: [PATCH] jfs: fix shift-out-of-bounds in dbJoin
dbJoin() can receive a corrupted newval from on-disk metadata that
exceeds the valid range for the BUDSIZE macro's shift operation.
When newval is larger than budmin + l2nleafs, the shift produces
undefined behavior detected by UBSAN.
Add a sanity check on newval before the shift to reject corrupted
values.
Reported-by: syzbot+fa603ae6b02658401ca7@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=fa603ae6b02658401ca7
Signed-off-by: Tristan Madani <tristan@talencesecurity.com>
---
fs/jfs/jfs_dmap.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/fs/jfs/jfs_dmap.c b/fs/jfs/jfs_dmap.c
index a841cf2..4ad9b34 100644
--- a/fs/jfs/jfs_dmap.c
+++ b/fs/jfs/jfs_dmap.c
@@ -2864,6 +2864,9 @@ static int dbJoin(dmtree_t *tp, int leafno, int newval, bool is_ctl)
if (newval >= tp->dmt_budmin) {
/* pickup a pointer to the leaves of the tree.
*/
+ if (newval > tp->dmt_budmin +
+ le32_to_cpu(tp->dmt_l2nleafs))
+ return -EIO;
leaf = tp->dmt_stree + le32_to_cpu(tp->dmt_leafidx);
/* try to join the specified leaf into a large binary
--
2.47.3
^ permalink raw reply related [flat|nested] 7+ messages in thread* Forwarded: Re: [syzbot] [jfs?] UBSAN: shift-out-of-bounds in dbJoin (2)
2025-12-06 16:31 [syzbot] [jfs?] UBSAN: shift-out-of-bounds in dbJoin (2) syzbot
` (3 preceding siblings ...)
2026-04-17 16:19 ` Forwarded: Re: [syzbot] UBSAN: " syzbot
@ 2026-04-17 19:19 ` syzbot
4 siblings, 0 replies; 7+ messages in thread
From: syzbot @ 2026-04-17 19:19 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: Re: [syzbot] [jfs?] UBSAN: shift-out-of-bounds in dbJoin (2)
Author: tristmd@gmail.com
#syz test: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
diff --git a/fs/jfs/jfs_dmap.c b/fs/jfs/jfs_dmap.c
index XXXXXXX..XXXXXXX 100644
--- a/fs/jfs/jfs_dmap.c
+++ b/fs/jfs/jfs_dmap.c
@@ -2770,6 +2770,10 @@ static int dbJoin(dmtree_t *tp, int leafno, int newval, bool is_ctl)
int budsz, buddy;
s8 *leaf;
+ if (newval < 0 ||
+ (newval >= tp->dmt_budmin && newval - tp->dmt_budmin >= 32))
+ return -EIO;
+
/* can the new leaf value require a join with other leaves ?
*/
if (newval >= tp->dmt_budmin) {
^ permalink raw reply [flat|nested] 7+ messages in thread