If the file system is corrupted, the header.stblindex variable may become greater than 127. Because of this, an array access out of bounds may occur: ------------[ cut here ]------------ UBSAN: array-index-out-of-bounds in fs/jfs/jfs_dtree.c:3096:10 index 237 is out of range for type 'struct dtslot[128]' CPU: 0 UID: 0 PID: 5822 Comm: syz-executor740 Not tainted 6.13.0-rc4-syzkaller-00110-g4099a71718b0 #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024 Call Trace: <TASK> __dump_stack lib/dump_stack.c:94 [inline] dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120 ubsan_epilogue lib/ubsan.c:231 [inline] __ubsan_handle_out_of_bounds+0x121/0x150 lib/ubsan.c:429 dtReadFirst+0x622/0xc50 fs/jfs/jfs_dtree.c:3096 dtReadNext fs/jfs/jfs_dtree.c:3147 [inline] jfs_readdir+0x9aa/0x3c50 fs/jfs/jfs_dtree.c:2862 wrap_directory_iterator+0x91/0xd0 fs/readdir.c:65 iterate_dir+0x571/0x800 fs/readdir.c:108 __do_sys_getdents64 fs/readdir.c:403 [inline] __se_sys_getdents64+0x1e2/0x4b0 fs/readdir.c:389 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x77/0x7f </TASK> ---[ end trace ]--- Add a stblindex check for corruption. Reported-by: syzbot <syzbot+9120834fc227768625ba@syzkaller.appspotmail.com> Closes: https://syzkaller.appspot.com/bug?extid=9120834fc227768625ba Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Cc: stable@vger.kernel.org Signed-off-by: Roman Smirnov <r.smirnov@omp.ru> Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>