[PATCH] erofs-utils: fsck: fix segmentation fault for file extraction

[Guo Xuenan]

Currently, we use fsckcfg.extract_path to record the path of file
to be extracted, when the name is too long, it will exceed the
fsckcfg.extract_path[PATH_MAX] array and segmentation fault may
occur.

Test and reproduce with the following script:
``` bash
#!/bin/bash
FSCK=`which fsck.erofs`
MKFS=`which mkfs.erofs`

IN_DIR=./src
$MKFS x.img ${IN_DIR}

get_dst_dir()
{
	local len=$1
	local perlen=$2
	local dst_dir=$(printf 'a%.0s' $(seq 1 $((perlen - 1))))
	local n=$((len / ${perlen}))
	local lastlen=$((len - perlen * n))
	local lastdir=$(printf 'a%.0s' $(seq 1 $lastlen))
	local outdir=""
	for x in `seq 1 $n`
	do
		outdir=${outdir}/${dst_dir}
	done

	[[ -n $lastdir ]] && outdir=${outdir}/${lastdir}
	echo ${outdir}
}

for n in `seq 4000 1 5000`
do
	dst_dir=$(get_dst_dir $n 255)
	echo ${#dst_dir}

	OUT_DIR="./${dst_dir}"
	rm -rf $(dirname $OUT_DIR) > /dev/null 2>&1
	mkdir -p $OUT_DIR
	$FSCK --extract=${OUT_DIR} x.img > /dev/null 2>&1
done
```

Fixes: f44043561491 ("erofs-utils: introduce fsck.erofs")
Fixes: b11f84f593f9 ("erofs-utils: fsck: convert to use erofs_iterate_dir()")
Fixes: 412c8f908132 ("erofs-utils: fsck: add --extract=X support to extract to path X")
Signed-off-by: Guo Xuenan <guoxuenan at huawei.com>
---
 fsck/main.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/fsck/main.c b/fsck/main.c
index a0377a7..47c01d8 100644
--- a/fsck/main.c
+++ b/fsck/main.c
@@ -131,6 +131,11 @@ static int erofsfsck_parse_options_cfg(int argc, char **argv)
 				while (len > 1 && optarg[len - 1] == '/')
 					len--;
 
+				if (len >= PATH_MAX) {
+					erofs_err("target directory name too long!");
+					return -ENAMETOOLONG;
+				}
+
 				fsckcfg.extract_path = malloc(PATH_MAX);
 				if (!fsckcfg.extract_path)
 					return -ENOMEM;
-- 
2.31.1