[PATCH] mkfs.ubifs: Fix heap corruption on LEB overrun

[Kevin Cernekee <cernekee@gmail.com>]

If max_leb_cnt (-c option) is set too low, set_lprops() will corrupt
the heap and may result in a scary looking crash:

$ bin/mkfs.ubifs -U -r romfs -o ubifs.img -m 512 -e 15360 -c 39
Error: max_leb_cnt too low (241 needed)
*** glibc detected *** bin/mkfs.ubifs: double free or corruption (!prev): 0x088fe070 ***
======= Backtrace: =========
/lib32/libc.so.6(+0x6c231)[0xf75fb231]
/lib32/libc.so.6(+0x6dab8)[0xf75fcab8]
/lib32/libc.so.6(cfree+0x6d)[0xf75ffb9d]
bin/mkfs.ubifs[0x804e801]
bin/mkfs.ubifs[0x804e94b]
bin/mkfs.ubifs[0x804e99d]
/lib32/libc.so.6(__libc_start_main+0xe6)[0xf75a5bd6]
bin/mkfs.ubifs(__fxstat64+0x55)[0x80491e1]
======= Memory map: ========
08048000-0805d000 r-xp 00000000 08:08 10012045                           /work/bin/mkfs.ubifs
0805d000-0805e000 rwxp 00015000 08:08 10012045                           /work/bin/mkfs.ubifs
088fe000-08945000 rwxp 00000000 00:00 0                                  [heap]
f73e1000-f73fe000 r-xp 00000000 08:05 2228842                            /usr/lib32/libgcc_s.so.1
f73fe000-f73ff000 r-xp 0001c000 08:05 2228842                            /usr/lib32/libgcc_s.so.1
f73ff000-f7400000 rwxp 0001d000 08:05 2228842                            /usr/lib32/libgcc_s.so.1
f7400000-f7421000 rwxp 00000000 00:00 0
f7421000-f7500000 ---p 00000000 00:00 0
f751c000-f758f000 rwxp 00000000 00:00 0
f758f000-f76e2000 r-xp 00000000 08:05 426288                             /lib32/libc-2.11.1.so
f76e2000-f76e3000 ---p 00153000 08:05 426288                             /lib32/libc-2.11.1.so
f76e3000-f76e5000 r-xp 00153000 08:05 426288                             /lib32/libc-2.11.1.so
f76e5000-f76e6000 rwxp 00155000 08:05 426288                             /lib32/libc-2.11.1.so
f76e6000-f76e9000 rwxp 00000000 00:00 0
f76e9000-f770d000 r-xp 00000000 08:05 426296                             /lib32/libm-2.11.1.so
f770d000-f770e000 r-xp 00023000 08:05 426296                             /lib32/libm-2.11.1.so
f770e000-f770f000 rwxp 00024000 08:05 426296                             /lib32/libm-2.11.1.so
f772a000-f772c000 rwxp 00000000 00:00 0
f772c000-f772d000 r-xp 00000000 00:00 0                                  [vdso]
f772d000-f7749000 r-xp 00000000 08:05 6062081                            /lib32/ld-2.11.1.so
f7749000-f774a000 r-xp 0001b000 08:05 6062081                            /lib32/ld-2.11.1.so
f774a000-f774b000 rwxp 0001c000 08:05 6062081                            /lib32/ld-2.11.1.so
ffb58000-ffb6d000 rwxp 00000000 00:00 0                                  [stack]
Aborted

New code aborts cleanly, and still calculates the number of LEBs
required:

$ bin/mkfs.ubifs -U -r romfs -o tmp/ubifs.img -m 512 -e 15360 -c 39
Error: max_leb_cnt too low (241 needed)
$ echo $?
255
$ bin/mkfs.ubifs -U -r romfs -o tmp/ubifs.img -m 512 -e 15360 -c 240
Error: max_leb_cnt too low (241 needed)
$ bin/mkfs.ubifs -U -r romfs -o tmp/ubifs.img -m 512 -e 15360 -c 241
$

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
---
 mkfs.ubifs/mkfs.ubifs.c |   10 +++++-----
 1 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/mkfs.ubifs/mkfs.ubifs.c b/mkfs.ubifs/mkfs.ubifs.c
index 9f2a226..60fe861 100644
--- a/mkfs.ubifs/mkfs.ubifs.c
+++ b/mkfs.ubifs/mkfs.ubifs.c
@@ -898,9 +898,11 @@ static void set_lprops(int lnum, int offs, int flags)
 	dirty = c->leb_size - free - ALIGN(offs, 8);
 	dbg_msg(3, "LEB %d free %d dirty %d flags %d", lnum, free, dirty,
 		flags);
-	c->lpt[i].free = free;
-	c->lpt[i].dirty = dirty;
-	c->lpt[i].flags = flags;
+	if (i < c->main_lebs) {
+		c->lpt[i].free = free;
+		c->lpt[i].dirty = dirty;
+		c->lpt[i].flags = flags;
+	}
 	c->lst.total_free += free;
 	c->lst.total_dirty += dirty;
 	if (flags & LPROPS_INDEX)
@@ -1902,8 +1904,6 @@ static int finalize_leb_cnt(void)
 {
 	c->leb_cnt = head_lnum;
 	if (c->leb_cnt > c->max_leb_cnt)
-		/* TODO: in this case it segfaults because buffer overruns - we
-		 * somewhere allocate smaller buffers - fix */
 		return err_msg("max_leb_cnt too low (%d needed)", c->leb_cnt);
 	c->main_lebs = c->leb_cnt - c->main_first;
 	if (verbose) {
-- 
1.7.0.4