Messages in this thread Patch in this message | | | Subject | Re: [PATCH] jffs2: Fix integer underflow in jffs2_rtime_compress | From | Hou Tao <> | Date | Thu, 23 Jan 2020 10:24:55 +0800 |
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Hi Richard,
On 2018/12/20 18:45, Richard Weinberger wrote: > Am Donnerstag, 20. Dezember 2018, 11:43:08 CET schrieb Hou Tao: >> >> On 2018/12/16 0:23, Richard Weinberger wrote: >>> The rtime compressor assumes that at least two bytes are >>> compressed. >>> If we try to compress just one byte, the loop condition will >>> wrap around and an out-of-bounds write happens. >>> >>> Cc: <stable@vger.kernel.org> >>> Signed-off-by: Richard Weinberger <richard@nod.at> >>> --- >>> fs/jffs2/compr_rtime.c | 3 +++ >>> 1 file changed, 3 insertions(+) >>> It seems that it doesn't incur any harm because the minimal allocated >> size will be 8-bytes and jffs2_rtime_compress() will write 2-bytes into >> the allocated buffer. > > Are you sure about that? I saw odd kernel behavior and KASAN complained too. >
Sorry for the later reply.
Yes. KASAN complains but it doesn't incur any harm because the minimal allocated size returned by kmalloc() will be 8-bytes.
But we better fix it, because it's bad to depend on the implementation of kmalloc().
It seems that mtd-utils has already fixed it years ago. Maybe we can use it directly ?
And your fix also looks good to me, so
Reviewed-by: Hou Tao <houtao1@huawei.com>
commit e8457f16306ad6e2c8708275bf42b5dfff40fffd Author: Enrico Scholz <enrico.scholz@sigma-chemnitz.de> Date: Thu Jun 24 15:02:40 2010 +0200
mkfs.jffs2: fix integer underflow in jffs2_rtime_compress()
When '*dstlen' is 0 or 1, comparison will return wrong result. Reported by valgrind as
==5919== Invalid write of size 1 ==5919== at 0x40564E: jffs2_rtime_compress (compr_rtime.c:51) ==5919== by 0x40676B: jffs2_compress (compr.c:246) ==5919== by 0x403EE4: recursive_populate_directory (mkfs.jffs2.c:884) ==5919== Address 0x4e1bdb1 is 0 bytes after a block of size 1 alloc'd ==5919== at 0x4A0515D: malloc (vg_replace_malloc.c:195) ==5919== by 0x40671C: jffs2_compress (compr.c:229) ==5919== by 0x403EE4: recursive_populate_directory (mkfs.jffs2.c:884)
Signed-off-by: Enrico Scholz <enrico.scholz@sigma-chemnitz.de> Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
diff --git a/compr_rtime.c b/compr_rtime.c index 131536c..5613963 100644 --- a/compr_rtime.c +++ b/compr_rtime.c @@ -32,7 +32,7 @@ static int jffs2_rtime_compress(unsigned char *data_in, unsigned char *cpage_out
memset(positions,0,sizeof(positions));
- while (pos < (*sourcelen) && outpos <= (*dstlen)-2) { + while (pos < (*sourcelen) && outpos+2 <= (*dstlen)) { int backpos, runlen=0; unsigned char value;
> Thanks, > //richard
> > > > . >
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