When an hfsplus image gets corrupted it might happen that the catalog
namelength field gets b0rked.  If we mount such an image the memcpy() in
hfsplus_cat_build_key_uni() writes more than the 255 that fit in the name
field.  Depending on the size of the overwritten data, we either only get
memory corruption or also trigger an oops like this:

[  221.628020] BUG: unable to handle kernel paging request at c82b0000
[  221.629066] IP: [<c022d4b1>] hfsplus_find_cat+0x10d/0x151
[  221.629066] *pde = 0ea29163 *pte = 082b0160
[  221.629066] Oops: 0002 [#1] PREEMPT DEBUG_PAGEALLOC
[  221.629066] Modules linked in:
[  221.629066]
[  221.629066] Pid: 4845, comm: mount Not tainted (2.6.27-rc4-00123-gd3ee1b40-dirty #28)
[  221.629066] EIP: 0060:[<c022d4b1>] EFLAGS: 00010206 CPU: 0
[  221.629066] EIP is at hfsplus_find_cat+0x10d/0x151
[  221.629066] EAX: 00000029 EBX: 00016210 ECX: 000042c2 EDX: 00000002
[  221.629066] ESI: c82d70ca EDI: c82b0000 EBP: c82d1bcc ESP: c82d199c
[  221.629066]  DS: 007b ES: 007b FS: 0000 GS: 0033 SS: 0068
[  221.629066] Process mount (pid: 4845, ti=c82d1000 task=c8224060 task.ti=c82d1000)
[  221.629066] Stack: c080b3c4 c82aa8f8 c82d19c2 00016210 c080b3be c82d1bd4 c82aa8f0 00000300
[  221.629066]        01000000 750008b1 74006e00 74006900 65006c00 c82d6400 c013bd35 c8224060
[  221.629066]        00000036 00000046 c82d19f0 00000082 c8224548 c8224060 00000036 c0d653cc
[  221.629066] Call Trace:
[  221.629066]  [<c013bd35>] ? trace_hardirqs_off+0xb/0xd
[  221.629066]  [<c013bca3>] ? trace_hardirqs_off_caller+0x14/0x9b
[  221.629066]  [<c013bd35>] ? trace_hardirqs_off+0xb/0xd
[  221.629066]  [<c013bca3>] ? trace_hardirqs_off_caller+0x14/0x9b
[  221.629066]  [<c013bd35>] ? trace_hardirqs_off+0xb/0xd
[  221.629066]  [<c0107aa3>] ? native_sched_clock+0x82/0x96
[  221.629066]  [<c01302d2>] ? __kernel_text_address+0x1b/0x27
[  221.629066]  [<c010487a>] ? dump_trace+0xca/0xd6
[  221.629066]  [<c0109e32>] ? save_stack_address+0x0/0x2c
[  221.629066]  [<c0109eaf>] ? save_stack_trace+0x1c/0x3a
[  221.629066]  [<c013b571>] ? save_trace+0x37/0x8d
[  221.629066]  [<c013b62e>] ? add_lock_to_list+0x67/0x8d
[  221.629066]  [<c013ea1c>] ? validate_chain+0x8a4/0x9f4
[  221.629066]  [<c013553d>] ? down+0xc/0x2f
[  221.629066]  [<c013f1f6>] ? __lock_acquire+0x68a/0x6e0
[  221.629066]  [<c013bd35>] ? trace_hardirqs_off+0xb/0xd
[  221.629066]  [<c013bca3>] ? trace_hardirqs_off_caller+0x14/0x9b
[  221.629066]  [<c013bd35>] ? trace_hardirqs_off+0xb/0xd
[  221.629066]  [<c0107aa3>] ? native_sched_clock+0x82/0x96
[  221.629066]  [<c013da5d>] ? mark_held_locks+0x43/0x5a
[  221.629066]  [<c013dc3a>] ? trace_hardirqs_on+0xb/0xd
[  221.629066]  [<c013dbf4>] ? trace_hardirqs_on_caller+0xf4/0x12f
[  221.629066]  [<c06abec8>] ? _spin_unlock_irqrestore+0x42/0x58
[  221.629066]  [<c013555c>] ? down+0x2b/0x2f
[  221.629066]  [<c022aa68>] ? hfsplus_iget+0xa0/0x154
[  221.629066]  [<c022b0b9>] ? hfsplus_fill_super+0x280/0x447
[  221.629066]  [<c0107aa3>] ? native_sched_clock+0x82/0x96
[  221.629066]  [<c013bca3>] ? trace_hardirqs_off_caller+0x14/0x9b
[  221.629066]  [<c013bca3>] ? trace_hardirqs_off_caller+0x14/0x9b
[  221.629066]  [<c013f1f6>] ? __lock_acquire+0x68a/0x6e0
[  221.629066]  [<c041c9e4>] ? string+0x2b/0x74
[  221.629066]  [<c041cd16>] ? vsnprintf+0x2e9/0x512
[  221.629066]  [<c010487a>] ? dump_trace+0xca/0xd6
[  221.629066]  [<c0109eaf>] ? save_stack_trace+0x1c/0x3a
[  221.629066]  [<c0109eaf>] ? save_stack_trace+0x1c/0x3a
[  221.629066]  [<c013b571>] ? save_trace+0x37/0x8d
[  221.629066]  [<c013b62e>] ? add_lock_to_list+0x67/0x8d
[  221.629066]  [<c013ea1c>] ? validate_chain+0x8a4/0x9f4
[  221.629066]  [<c01354d3>] ? up+0xc/0x2f
[  221.629066]  [<c013f1f6>] ? __lock_acquire+0x68a/0x6e0
[  221.629066]  [<c013bd35>] ? trace_hardirqs_off+0xb/0xd
[  221.629066]  [<c013bca3>] ? trace_hardirqs_off_caller+0x14/0x9b
[  221.629066]  [<c013bd35>] ? trace_hardirqs_off+0xb/0xd
[  221.629066]  [<c0107aa3>] ? native_sched_clock+0x82/0x96
[  221.629066]  [<c041cfb7>] ? snprintf+0x1b/0x1d
[  221.629066]  [<c01ba466>] ? disk_name+0x25/0x67
[  221.629066]  [<c0183960>] ? get_sb_bdev+0xcd/0x10b
[  221.629066]  [<c016ad92>] ? kstrdup+0x2a/0x4c
[  221.629066]  [<c022a7b3>] ? hfsplus_get_sb+0x13/0x15
[  221.629066]  [<c022ae39>] ? hfsplus_fill_super+0x0/0x447
[  221.629066]  [<c0183583>] ? vfs_kern_mount+0x3b/0x76
[  221.629066]  [<c0183602>] ? do_kern_mount+0x32/0xba
[  221.629066]  [<c01960d4>] ? do_new_mount+0x46/0x74
[  221.629066]  [<c0196277>] ? do_mount+0x175/0x193
[  221.629066]  [<c013dbf4>] ? trace_hardirqs_on_caller+0xf4/0x12f
[  221.629066]  [<c01663b2>] ? __get_free_pages+0x1e/0x24
[  221.629066]  [<c06ac07b>] ? lock_kernel+0x19/0x8c
[  221.629066]  [<c01962e6>] ? sys_mount+0x51/0x9b
[  221.629066]  [<c01962f9>] ? sys_mount+0x64/0x9b
[  221.629066]  [<c01038bd>] ? sysenter_do_call+0x12/0x31
[  221.629066]  =======================
[  221.629066] Code: 89 c2 c1 e2 08 c1 e8 08 09 c2 8b 85 e8 fd ff ff 66 89 50 06 89 c7 53 83 c7 08 56 57 68 c4 b3 80 c0 e8 8c 5c ef ff 89 d9 c1 e9 02 <f3> a5 89 d9 83 e1 03 74 02 f3 a4 83 c3 06 8b 95 e8 fd ff ff 0f
[  221.629066] EIP: [<c022d4b1>] hfsplus_find_cat+0x10d/0x151 SS:ESP 0068:c82d199c
[  221.629066] ---[ end trace e417a1d67f0d0066 ]---

Since hfsplus_cat_build_key_uni() returns void and only has one callsite,
the check is performed at the callsite.
Signed-off-by: Eric Sesterhenn <snakebyte@gmx.de>
Reviewed-by: Pekka Enberg <penberg@cs.helsinki.fi>
Cc: Roman Zippel <zippel@linux-m68k.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>