A corrupted JFS filesystem image can cause a state where the block allocation map (bmap) and the dmap pages are out of sync. Specifically, if a dmap page's `dp->start` is corrupted, it can lead to a mismatch during block allocation or update operations. The block allocator calculates the returned block number based on `dp->start` (i.e., `dp->start + block_index`), while the bitmap update is derived from the block's relative position within the dmap. If `dp->start` does not match the expected start block number for that dmap's position in the bmap, the allocator may return a block number that is already in use (e.g., as an inode table block or metadata), while marking a completely different block as allocated. This mismatch leads to duplicate allocations. When a thread later attempts to lock this duplicate block (for example, during a directory btree split), `txLock()` detects a metapage conflict because the block is already locked for another purpose, triggering a kernel BUG: kernel BUG at fs/jfs/jfs_txnmgr.c:836! Oops: invalid opcode: 0000 [#1] SMP KASAN NOPTI RIP: 0010:txLock+0x1cc3/0x1d10 fs/jfs/jfs_txnmgr.c:836 Call Trace: dtSplitRoot+0x38d/0x18a0 fs/jfs/jfs_dtree.c:1924 dtSplitUp fs/jfs/jfs_dtree.c:990 [inline] dtInsert+0xeb2/0x5890 fs/jfs/jfs_dtree.c:868 jfs_create+0x730/0xae0 fs/jfs/namei.c:138 vfs_create+0x2c4/0x450 fs/namei.c:4202 filename_mknodat+0x3e8/0x660 fs/namei.c:5181 ... To fix this, validate that the `dp->start` of the dmap page matches the expected start block number before performing block map operations. Rejecting a mismatched start with `-EIO` prevents duplicate allocations before `txLock()` is reached. Assisted-by: Gemini:gemini-3.5-flash Gemini:gemini-3.1-pro-preview syzbot Reported-by: syzbot+a843f6ae2130a987d63b@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=a843f6ae2130a987d63b Link: https://syzkaller.appspot.com/ai_job?id=bdbf4b4d-3729-479d-89c3-0cee1fcde974 To: To: "Dave Kleikamp" Cc: "Kees Cook" Cc: Cc: "Yun Zhou" Cc: "Zheng Yu" --- v3: - Renamed the patch to "jfs: validate dmap start before block map operations". - Simplified dbValidateDmap() to only validate that the dmap dp->start matches the expected start block number, removing unproven integrity checks. - Updated the commit description to explain the exact root cause of the selection/update mismatch and how validating dp->start prevents duplicate allocations before txLock() is reached. v2: - Replaced the approach of propagating errors from txLock() with proactive dmap validation. - Introduced dbValidateDmap() to check dmap page integrity (nblocks, nfree, start address, and tree structure). - Integrated dmap validation into dbFree(), dbUpdatePMap(), dbAlloc(), dbExtend(), dbAllocCtl(), dbAllocBottomUp(), and dbExtendFS(). - Reverted return type changes for functions in jfs_dtree.c and jfs_xtree.c from the previous version. https://lore.kernel.org/all/ff86d803-d687-48f6-9cc2-f3d35b27a666@mail.kernel.org/T/ v1: https://lore.kernel.org/all/9d2eba88-93bf-4f3c-a3b2-b554e1fffe80@mail.kernel.org/T/ --- diff --git a/fs/jfs/jfs_dmap.c b/fs/jfs/jfs_dmap.c index a841cf21d..f15954c1f 100644 --- a/fs/jfs/jfs_dmap.c +++ b/fs/jfs/jfs_dmap.c @@ -98,6 +98,9 @@ static int blkstol2(s64 nb); static int cntlz(u32 value); static int cnttz(u32 word); +static bool dbValidateDmap(struct super_block *sb, const struct dmap *dp, + s64 expected_start); + static int dbAllocDmapBU(struct bmap * bmp, struct dmap * dp, s64 blkno, int nblocks); static int dbInitDmap(struct dmap * dp, s64 blkno, int nblocks); @@ -476,6 +479,12 @@ int dbFree(struct inode *ip, s64 blkno, s64 nblocks) } dp = (struct dmap *) mp->data; + if (!dbValidateDmap(ip->i_sb, dp, blkno & ~(s64)(BPERDMAP - 1))) { + release_metapage(mp); + IREAD_UNLOCK(ipbmap); + return -EIO; + } + /* determine the number of blocks to be freed from * this dmap. */ @@ -568,6 +577,13 @@ dbUpdatePMap(struct inode *ipbmap, if (mp == NULL) return -EIO; metapage_wait_for_io(mp); + + if (!dbValidateDmap(ipbmap->i_sb, + (struct dmap *) mp->data, + blkno & ~(s64)(BPERDMAP - 1))) { + release_metapage(mp); + return -EIO; + } } dp = (struct dmap *) mp->data; @@ -886,6 +902,11 @@ int dbAlloc(struct inode *ip, s64 hint, s64 nblocks, s64 * results) dp = (struct dmap *) mp->data; + if (!dbValidateDmap(ip->i_sb, dp, blkno & ~(s64)(BPERDMAP - 1))) { + release_metapage(mp); + goto read_unlock; + } + /* first, try to satisfy the allocation request with the * blocks beginning at the hint. */ @@ -1118,6 +1139,12 @@ static int dbExtend(struct inode *ip, s64 blkno, s64 nblocks, s64 addnblocks) dp = (struct dmap *) mp->data; + if (!dbValidateDmap(ip->i_sb, dp, extblkno & ~(s64)(BPERDMAP - 1))) { + release_metapage(mp); + IREAD_UNLOCK(ipbmap); + return -EIO; + } + /* try to allocate the blocks immediately following the * current allocation. */ @@ -1902,7 +1929,7 @@ dbAllocCtl(struct bmap * bmp, s64 nblocks, int l2nb, s64 blkno, s64 * results) return -EIO; dp = (struct dmap *) mp->data; - if (dp->tree.budmin < 0) { + if (!dbValidateDmap(bmp->db_ipbmap->i_sb, dp, blkno & ~(s64)(BPERDMAP - 1))) { release_metapage(mp); return -EIO; } @@ -1936,6 +1963,12 @@ dbAllocCtl(struct bmap * bmp, s64 nblocks, int l2nb, s64 blkno, s64 * results) } dp = (struct dmap *) mp->data; + if (!dbValidateDmap(bmp->db_ipbmap->i_sb, dp, b & ~(s64)(BPERDMAP - 1))) { + release_metapage(mp); + rc = -EIO; + goto backout; + } + /* the dmap better be all free. */ if (dp->tree.stree[ROOT] != L2BPERDMAP) { @@ -1993,6 +2026,11 @@ dbAllocCtl(struct bmap * bmp, s64 nblocks, int l2nb, s64 blkno, s64 * results) } dp = (struct dmap *) mp->data; + if (!dbValidateDmap(bmp->db_ipbmap->i_sb, dp, b & ~(s64)(BPERDMAP - 1))) { + release_metapage(mp); + continue; + } + /* free the blocks is this dmap. */ if (dbFreeDmap(bmp, dp, b, BPERDMAP)) { @@ -2134,6 +2172,18 @@ static int dbAllocDmap(struct bmap * bmp, struct dmap * dp, s64 blkno, return (rc); } +static bool dbValidateDmap(struct super_block *sb, const struct dmap *dp, + s64 expected_start) +{ + if (le64_to_cpu(dp->start) != expected_start) { + jfs_error(sb, "corrupt dmap page: start %lld expected %lld\n", + (long long)le64_to_cpu(dp->start), + (long long)expected_start); + return false; + } + + return true; +} /* * NAME: dbFreeDmap() @@ -3308,6 +3358,12 @@ int dbAllocBottomUp(struct inode *ip, s64 blkno, s64 nblocks) } dp = (struct dmap *) mp->data; + if (!dbValidateDmap(ip->i_sb, dp, blkno & ~(s64)(BPERDMAP - 1))) { + release_metapage(mp); + IREAD_UNLOCK(ipbmap); + return -EIO; + } + /* determine the number of blocks to be allocated from * this dmap. */ base-commit: dc59e4fea9d83f03bad6bddf3fa2e52491777482 -- This is an AI-generated patch subject to moderation. 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