From: Aditya Dutt duttaditya18@gmail.com
[ Upstream commit 5dff41a86377563f7a2b968aae00d25b4ceb37c9 ]
stbl is s8 but it must contain offsets into slot which can go from 0 to 127.
Added a bound check for that error and return -EIO if the check fails. Also make jfs_readdir return with error if add_missing_indices returns with an error.
Reported-by: syzbot+b974bd41515f770c608b@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com./bug?extid=b974bd41515f770c608b Signed-off-by: Aditya Dutt duttaditya18@gmail.com Signed-off-by: Dave Kleikamp dave.kleikamp@oracle.com Signed-off-by: Sasha Levin sashal@kernel.org ---
**YES** This commit should be backported to stable kernel trees. Here's my detailed analysis: ## Security and Stability Impact 1. **Critical Array-Index-Out-of-Bounds Fix**: The commit addresses a serious array- index-out-of-bounds vulnerability in the JFS filesystem's `add_missing_indices()` function at `fs/jfs/jfs_dtree.c:2648`. The code was accessing `p->slot[stbl[i]]` without validating that `stbl[i]` is within valid bounds (0-127). 2. **Consistent with Established Pattern**: This fix follows the exact same pattern as **all 5 similar commits** that were marked as "Backport Status: YES": - Similar Commits #1, #2, #3 all add bounds checking for `stbl[i] < 0 || stbl[i] > 127` - Similar Commits #4, #5 add bounds checking for array indices in JFS - All were successfully backported due to their security importance 3. **Syzbot- Reported Vulnerability**: The commit fixes a vulnerability reported by syzbot (`syzbot+b974bd41515f770c608b@syzkaller.appspotmail.com`), indicating this is a real exploitable issue found through fuzzing. ## Code Analysis **Key Changes Made:** 1. **Bounds Check Addition**: Added validation `if (stbl[i] < 0)` before accessing `p->slot[stbl[i]]` 2. **Error Handling**: Changed `add_missing_indices()` from `void` to `int` return type to propagate errors 3. **Proper Error Propagation**: Modified `jfs_readdir()` to check return value and exit on error: `if ((rc = add_missing_indices(ip, bn))) goto out;` 4. **Transaction Cleanup**: Added `txAbort(tid, 0)` on error path to properly clean up the transaction **Technical Context:** - `stbl` is declared as `s8 *` (signed 8-bit array) but must contain valid slot indices (0-127) - `DTPAGEMAXSLOT` is defined as 128, so valid indices are 0-127 - Negative values in `stbl[i]` cause array-index-out-of-bounds when accessing `p->slot[stbl[i]]` ## Backport Criteria Assessment ✅ **Fixes Important Bug**: Prevents potential kernel crashes and security issues ✅ **Small and Contained**: Limited to one function with clear, minimal changes ✅ **No Side Effects**: Only adds bounds checking and error handling ✅ **No Architectural Changes**: Preserves existing logic flow ✅ **Critical Subsystem**: Filesystem corruption/crashes affect system stability ✅ **Clear Pattern**: Identical to 5 other successfully backported JFS fixes ✅ **Minimal Regression Risk**: Only adds safety checks, doesn't change core logic ✅ **Confined to Subsystem**: Changes isolated to JFS dtree handling ## Existing Infrastructure The kernel already has extensive bounds checking for `stbl` indices throughout `jfs_dtree.c`: - Line 2895-2898: `if (stbl[i] < 0 || stbl[i] > 127)` in `jfs_readdir()` - Line 3099-3102: `if (stbl[0] < 0 || stbl[0] > 127)` in `dtReadFirst()` - Line 637-640: `if (stbl[index] < 0)` in search functions This commit simply extends the same pattern to the previously missed `add_missing_indices()` function, maintaining consistency with the existing codebase security measures. The fix is essential for preventing potential kernel crashes and maintaining filesystem integrity, making it an ideal candidate for stable tree backporting.
fs/jfs/jfs_dtree.c | 18 +++++++++++++++--- 1 file changed, 15 insertions(+), 3 deletions(-)
diff --git a/fs/jfs/jfs_dtree.c b/fs/jfs/jfs_dtree.c index 417d1c2fc2911..27ca98614b0bb 100644 --- a/fs/jfs/jfs_dtree.c +++ b/fs/jfs/jfs_dtree.c @@ -2909,7 +2909,7 @@ void dtInitRoot(tid_t tid, struct inode *ip, u32 idotdot) * fsck.jfs should really fix this, but it currently does not. * Called from jfs_readdir when bad index is detected. */ -static void add_missing_indices(struct inode *inode, s64 bn) +static int add_missing_indices(struct inode *inode, s64 bn) { struct ldtentry *d; struct dt_lock *dtlck; @@ -2918,7 +2918,7 @@ static void add_missing_indices(struct inode *inode, s64 bn) struct lv *lv; struct metapage *mp; dtpage_t *p; - int rc; + int rc = 0; s8 *stbl; tid_t tid; struct tlock *tlck; @@ -2943,6 +2943,16 @@ static void add_missing_indices(struct inode *inode, s64 bn)
stbl = DT_GETSTBL(p); for (i = 0; i < p->header.nextindex; i++) { + if (stbl[i] < 0) { + jfs_err("jfs: add_missing_indices: Invalid stbl[%d] = %d for inode %ld, block = %lld", + i, stbl[i], (long)inode->i_ino, (long long)bn); + rc = -EIO; + + DT_PUTPAGE(mp); + txAbort(tid, 0); + goto end; + } + d = (struct ldtentry *) &p->slot[stbl[i]]; index = le32_to_cpu(d->index); if ((index < 2) || (index >= JFS_IP(inode)->next_index)) { @@ -2960,6 +2970,7 @@ static void add_missing_indices(struct inode *inode, s64 bn) (void) txCommit(tid, 1, &inode, 0); end: txEnd(tid); + return rc; }
/* @@ -3313,7 +3324,8 @@ int jfs_readdir(struct file *file, struct dir_context *ctx) }
if (fix_page) { - add_missing_indices(ip, bn); + if ((rc = add_missing_indices(ip, bn))) + goto out; page_fixed = 1; }