jfs: fix array-index-out-of-bounds in diNewExt

[ Upstream commit 49f9637aafa6e63ba686c13cb8549bf5e6920402 ]

[Syz report]
UBSAN: array-index-out-of-bounds in fs/jfs/jfs_imap.c:2360:2
index -878706688 is out of range for type 'struct iagctl[128]'
CPU: 1 PID: 5065 Comm: syz-executor282 Not tainted 6.7.0-rc4-syzkaller-00009-gbee0e7762ad2 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/10/2023
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x1e7/0x2d0 lib/dump_stack.c:106
 ubsan_epilogue lib/ubsan.c:217 [inline]
 __ubsan_handle_out_of_bounds+0x11c/0x150 lib/ubsan.c:348
 diNewExt+0x3cf3/0x4000 fs/jfs/jfs_imap.c:2360
 diAllocExt fs/jfs/jfs_imap.c:1949 [inline]
 diAllocAG+0xbe8/0x1e50 fs/jfs/jfs_imap.c:1666
 diAlloc+0x1d3/0x1760 fs/jfs/jfs_imap.c:1587
 ialloc+0x8f/0x900 fs/jfs/jfs_inode.c:56
 jfs_mkdir+0x1c5/0xb90 fs/jfs/namei.c:225
 vfs_mkdir+0x2f1/0x4b0 fs/namei.c:4106
 do_mkdirat+0x264/0x3a0 fs/namei.c:4129
 __do_sys_mkdir fs/namei.c:4149 [inline]
 __se_sys_mkdir fs/namei.c:4147 [inline]
 __x64_sys_mkdir+0x6e/0x80 fs/namei.c:4147
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x45/0x110 arch/x86/entry/common.c:82
 entry_SYSCALL_64_after_hwframe+0x63/0x6b
RIP: 0033:0x7fcb7e6a0b57
Code: ff ff 77 07 31 c0 c3 0f 1f 40 00 48 c7 c2 b8 ff ff ff f7 d8 64 89 02 b8 ff ff ff ff c3 66 0f 1f 44 00 00 b8 53 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffd83023038 EFLAGS: 00000286 ORIG_RAX: 0000000000000053
RAX: ffffffffffffffda RBX: 00000000ffffffff RCX: 00007fcb7e6a0b57
RDX: 00000000000a1020 RSI: 00000000000001ff RDI: 0000000020000140
RBP: 0000000020000140 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000286 R12: 00007ffd830230d0
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000

[Analysis]
When the agstart is too large, it can cause agno overflow.

[Fix]
After obtaining agno, if the value is invalid, exit the subsequent process.

Reported-and-tested-by: syzbot+553d90297e6d2f50dbc7@syzkaller.appspotmail.com
Signed-off-by: Edward Adam Davis <eadavis@qq.com>

Modified the test from agno > MAXAG to agno >= MAXAG based on linux-next
report by kernel test robot (Dan Carpenter).

Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

fs/jfs/jfs_imap.c

@@ -2179,6 +2179,9 @@ static int diNewExt(struct inomap * imap, struct iag * iagp, int extno)
 	/* get the ag and iag numbers for this iag.
 	 */
 	agno = BLKTOAG(le64_to_cpu(iagp->agstart), sbi);
+	if (agno >= MAXAG || agno < 0)
+		return -EIO;
+
 	iagno = le32_to_cpu(iagp->iagnum);
 
 	/* check if this is the last free extent within the