[PATCH RFC v3] jfs: validate BT_ROOT flag in xt_getpage and DT_GETPAGE
"syzbot" <[email protected]> Wed, 15 Jul 2026 15:28:34 +0000 (UTC)
| Newsgroups | dev.linux.lists.syzbot |
|---|---|
| Message-ID | <[email protected]> |
A corrupted JFS image can trick the kernel into calling release_metapage()
on a pseudo-metapage embedded within the inode, leading to an out-of-bounds
memory access and a spinlock crash.
When operating on the root page of an xtree or dtree (which is stored
inline within the inode), JFS doesn't use a real struct metapage. Instead,
BT_GETPAGE() sets the metapage pointer to the address of
JFS_IP(ip)->bxflag. Because this is a pseudo-metapage, it does not have a
valid wait_queue_head_t wait field. Accessing mp->wait reads out-of-bounds
memory in struct jfs_inode_info.
In xt_getpage(), the code validates nextindex and maxentry, but it fails to
verify that the BT_ROOT flag is set in p->header.flag for the root page (bn
== 0). If the inline xtree root page has a corrupted header.flag where
BT_ROOT is missing, xtTruncate() will mistakenly treat the root page as a
regular leaf page and call discard_metapage(mp).
Unlike XT_PUTPAGE() which safely checks !BT_IS_ROOT(mp) before releasing,
discard_metapage() calls release_metapage(mp) directly. This assumes mp is
a real metapage and calls unlock_metapage(mp), which executes
wake_up(&mp->wait), accessing garbage memory and resulting in a spinlock
bad magic BUG or UBSAN out-of-bounds array access.
Fix this by enforcing the invariant that the BT_ROOT flag is set if and
only if bn == 0 in both xt_getpage() and DT_GETPAGE().
BUG: spinlock bad magic on CPU#1, syz-executor/6078
lock: 0xffff8881f55f1b48, .magic: ffffffff, .owner: /-1902340672,
.owner_cpu: 768
CPU: 1 UID: 0 PID: 6078 Comm: syz-executor Not tainted syzkaller #1
PREEMPT(full)
Call Trace:
<TASK>
dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
spin_bug kernel/locking/spinlock_debug.c:78 [inline]
debug_spin_lock_before kernel/locking/spinlock_debug.c:86 [inline]
do_raw_spin_lock+0x1e5/0x2f0 kernel/locking/spinlock_debug.c:115
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:133 [inline]
_raw_spin_lock_irqsave+0x4c/0x60 kernel/locking/spinlock.c:166
__wake_up_common_lock+0x30/0x1f0 kernel/sched/wait.c:124
unlock_metapage fs/jfs/jfs_metapage.c:40 [inline]
release_metapage+0x131/0xa60 fs/jfs/jfs_metapage.c:872
xtTruncate+0xeaa/0x2eb0 fs/jfs/jfs_xtree.c:-1
jfs_free_zero_link+0x35b/0x4c0 fs/jfs/namei.c:760
jfs_evict_inode+0x356/0x430 fs/jfs/inode.c:159
evict+0x624/0xb50 fs/inode.c:841
...
</TASK>
UBSAN: array-index-out-of-bounds in kernel/locking/qspinlock.h:68:9
index 8945 is out of range for type 'unsigned long[8]'
CPU: 1 UID: 0 PID: 6078 Comm: syz-executor Not tainted syzkaller #1
PREEMPT(full)
Call Trace:
<TASK>
dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
ubsan_epilogue+0xa/0x30 lib/ubsan.c:233
__ubsan_handle_out_of_bounds+0xe8/0xf0 lib/ubsan.c:455
decode_tail kernel/locking/qspinlock.h:68 [inline]
__pv_queued_spin_lock_slowpath+0xaf3/0xbc0 kernel/locking/qspinlock.c:285
pv_queued_spin_lock_slowpath arch/x86/include/asm/paravirt-spinlock.h:35
[inline]
queued_spin_lock_slowpath arch/x86/include/asm/paravirt-spinlock.h:66
[inline]
queued_spin_lock include/asm-generic/qspinlock.h:114 [inline]
do_raw_spin_lock+0x26c/0x2f0 kernel/locking/spinlock_debug.c:116
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:133 [inline]
_raw_spin_lock_irqsave+0x4c/0x60 kernel/locking/spinlock.c:166
__wake_up_common_lock+0x30/0x1f0 kernel/sched/wait.c:124
unlock_metapage fs/jfs/jfs_metapage.c:40 [inline]
release_metapage+0x131/0xa60 fs/jfs/jfs_metapage.c:872
xtTruncate+0xeaa/0x2eb0 fs/jfs/jfs_xtree.c:-1
...
</TASK>
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Assisted-by: Gemini:gemini-3.1-pro-preview Gemini:gemini-3-flash-preview syzbot
Reported-by: [email protected]
Closes: https://syzkaller.appspot.com/bug?extid=e380443eaa59bfb75a84
Link: https://syzkaller.appspot.com/ai_job?id=20a14f45-b85b-4c13-8896-26c43b87a29b
To: <[email protected]>
To: "Dave Kleikamp" <[email protected]>
Cc: "Arnd Bergmann" <[email protected]>
Cc: <[email protected]>
Cc: "Yun Zhou" <[email protected]>
Cc: "Zheng Yu" <[email protected]>
---
v3:
- Validated root/non-root invariant failures and non-root dtpage integrity failures.
- Removed '------------[ cut here ]------------' from the commit message.
v2:
- Combined the BT_ROOT flag validation with the existing page integrity check in DT_GETPAGE.
- Unified the error message in DT_GETPAGE for both root and leaf page corruption.
https://lore.kernel.org/all/[email protected]/T/
v1:
https://lore.kernel.org/all/[email protected]/T/
---
diff --git a/fs/jfs/jfs_dtree.c b/fs/jfs/jfs_dtree.c
index ac0f79faf..2b6bdea1f 100644
--- a/fs/jfs/jfs_dtree.c
+++ b/fs/jfs/jfs_dtree.c
@@ -111,19 +111,20 @@ struct dtsplit {
#define DT_PAGE(IP, MP) BT_PAGE(IP, MP, dtpage_t, i_dtroot)
/* get page buffer for specified block address */
-#define DT_GETPAGE(IP, BN, MP, SIZE, P, RC) \
-do { \
- BT_GETPAGE(IP, BN, MP, dtpage_t, SIZE, P, RC, i_dtroot); \
- if (!(RC)) { \
- if ((BN) && !check_dtpage(P)) { \
- BT_PUTPAGE(MP); \
- jfs_error((IP)->i_sb, \
- "DT_GETPAGE: dtree page corrupt\n"); \
- MP = NULL; \
- RC = -EIO; \
- } \
- } \
-} while (0)
+#define DT_GETPAGE(IP, BN, MP, SIZE, P, RC) \
+ do { \
+ BT_GETPAGE(IP, BN, MP, dtpage_t, SIZE, P, RC, i_dtroot); \
+ if (!(RC)) { \
+ if ((((BN) == 0) != !!((P)->header.flag & BT_ROOT)) || \
+ ((BN) && !check_dtpage(P))) { \
+ BT_PUTPAGE(MP); \
+ jfs_error((IP)->i_sb, \
+ "DT_GETPAGE: dtree page corrupt\n"); \
+ MP = NULL; \
+ RC = -EIO; \
+ } \
+ } \
+ } while (0)
/* for consistency */
#define DT_PUTPAGE(MP) BT_PUTPAGE(MP)
diff --git a/fs/jfs/jfs_xtree.c b/fs/jfs/jfs_xtree.c
index 28c3cf960..6d960dd96 100644
--- a/fs/jfs/jfs_xtree.c
+++ b/fs/jfs/jfs_xtree.c
@@ -118,10 +118,11 @@ static inline xtpage_t *xt_getpage(struct inode *ip, s64 bn, struct metapage **m
if (rc)
return ERR_PTR(rc);
if ((le16_to_cpu(p->header.nextindex) < XTENTRYSTART) ||
- (le16_to_cpu(p->header.nextindex) >
- le16_to_cpu(p->header.maxentry)) ||
- (le16_to_cpu(p->header.maxentry) >
- ((bn == 0) ? XTROOTMAXSLOT : PSIZE >> L2XTSLOTSIZE))) {
+ (le16_to_cpu(p->header.nextindex) >
+ le16_to_cpu(p->header.maxentry)) ||
+ (le16_to_cpu(p->header.maxentry) >
+ ((bn == 0) ? XTROOTMAXSLOT : PSIZE >> L2XTSLOTSIZE)) ||
+ ((bn == 0) != !!(p->header.flag & BT_ROOT))) {
jfs_error(ip->i_sb, "xt_getpage: xtree page corrupt\n");
BT_PUTPAGE(*mp);
*mp = NULL;
base-commit: 8cd9520d35a6c38db6567e97dd93b1f11f185dc6
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