7.3-stable review patch. If anyone has any objections, please let me know. ------------------ From: YANXIN LI commit 1eff23433e73d7da4f9e3529d2701e34962b161f upstream. ufs1_read_inode() and ufs2_read_inode() copy the untrusted 64-bit on-disk size into inode->i_size. ufs_last_byte() then truncates that value to an unsigned int before calculating the valid extent of a directory folio. A directory size of exactly 4 GiB is truncated to zero. In ufs_find_entry(), subtracting the requested record length from that zero forms an endpoint almost 4 GiB beyond the mapped folio. A crafted UFS2 image produces: BUG: KASAN: use-after-free in ufs_find_entry+0x583/0x6e0 [ufs] Read of size 1 ... ufs_find_entry ufs_inode_by_name ufs_lookup __lookup_slow path_lookupat The KASAN classification reflects that the adjacent physical page was free; the source-level operation is an out-of-folio read. A controlled UFS1 test with CONFIG_UFS_FS_WRITE enabled also made ufs_find_entry() return a directory entry from an adjacent anonymous page. unlink() then passed that pointer to ufs_delete_entry(), which cleared the adjacent page's 3 2-bit d_ino. This write result reproduced three out of three times. UFS normally requires a privileged mount path. A relevant boundary is a privileged automounter or image-processing service handling an attacker-supplied filesystem. The write primitive additionally requires UFS1 to be mounted read-write with CONFIG_UFS_FS_WRITE enabled; the read is reachable with read-only UFS2. Keep the intermediate size arithmetic at 64 bits so non-final pages are bounded at PAGE_SIZE. With this change, the same controlled tests reach the real on-disk directory entry and produce no adjacent-page write or KASAN report. A reproducer and full validation logs are available on request. The vulnerable helper is present in v7.2-rc3, v7.1, v6.18.38, v6.12.95, v6.6.111, and upstream master at 1229e2e57a5c. Runtime reproduction and fix validation were performed in an x86-64 QEMU guest running v7.2-rc3 with generic KASAN. Fixes: b71034e5e67d ("[PATCH] ufs: directory and page cache: from blocks to pages") Cc: stable@vger.kernel.org Signed-off-by: YANXIN LI Link: https://patch.msgid.link/20260718190300.867109-1-fadouse@pm.me Reviewed-by: Jan Kara Signed-off-by: Christian Brauner (Amutable) Signed-off-by: Greg Kroah-Hartman --- fs/ufs/dir.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/fs/ufs/dir.c +++ b/fs/ufs/dir.c @@ -213,7 +213,7 @@ fail: static unsigned ufs_last_byte(struct inode *inode, unsigned long page_nr) { - unsigned last_byte = inode->i_size; + u64 last_byte = inode->i_size; last_byte -= page_nr << PAGE_SHIFT; if (last_byte > PAGE_SIZE)