Patch "erofs: fix buffer copy overflow of ztailpacking feature" has been added to the 5.18-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    erofs: fix buffer copy overflow of ztailpacking feature

to the 5.18-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     erofs-fix-buffer-copy-overflow-of-ztailpacking-featu.patch
and it can be found in the queue-5.18 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit d343154ccc4046d5bce3589ed99d3944e38c5bd0
Author: Gao Xiang <hsiangkao@xxxxxxxxxxxxxxxxx>
Date:   Thu May 12 19:58:33 2022 +0800

    erofs: fix buffer copy overflow of ztailpacking feature
    
    [ Upstream commit dcbe6803fffd387f72b48c2373b5f5ed12a5804b ]
    
    I got some KASAN report as below:
    
    [   46.959738] ==================================================================
    [   46.960430] BUG: KASAN: use-after-free in z_erofs_shifted_transform+0x2bd/0x370
    [   46.960430] Read of size 4074 at addr ffff8880300c2f8e by task fssum/188
    ...
    [   46.960430] Call Trace:
    [   46.960430]  <TASK>
    [   46.960430]  dump_stack_lvl+0x41/0x5e
    [   46.960430]  print_report.cold+0xb2/0x6b7
    [   46.960430]  ? z_erofs_shifted_transform+0x2bd/0x370
    [   46.960430]  kasan_report+0x8a/0x140
    [   46.960430]  ? z_erofs_shifted_transform+0x2bd/0x370
    [   46.960430]  kasan_check_range+0x14d/0x1d0
    [   46.960430]  memcpy+0x20/0x60
    [   46.960430]  z_erofs_shifted_transform+0x2bd/0x370
    [   46.960430]  z_erofs_decompress_pcluster+0xaae/0x1080
    
    The root cause is that the tail pcluster won't be a complete filesystem
    block anymore. So if ztailpacking is used, the second part of an
    uncompressed tail pcluster may not be ``rq->pageofs_out``.
    
    Fixes: ab749badf9f4 ("erofs: support unaligned data decompression")
    Fixes: cecf864d3d76 ("erofs: support inline data decompression")
    Reviewed-by: Yue Hu <huyue2@xxxxxxxxxxx>
    Reviewed-by: Chao Yu <chao@xxxxxxxxxx>
    Link: https://lore.kernel.org/r/20220512115833.24175-1-hsiangkao@xxxxxxxxxxxxxxxxx
    Signed-off-by: Gao Xiang <hsiangkao@xxxxxxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/fs/erofs/decompressor.c b/fs/erofs/decompressor.c
index 3efa686c7644..0e0d1fc0f130 100644
--- a/fs/erofs/decompressor.c
+++ b/fs/erofs/decompressor.c
@@ -322,6 +322,7 @@ static int z_erofs_shifted_transform(struct z_erofs_decompress_req *rq,
 		PAGE_ALIGN(rq->pageofs_out + rq->outputsize) >> PAGE_SHIFT;
 	const unsigned int righthalf = min_t(unsigned int, rq->outputsize,
 					     PAGE_SIZE - rq->pageofs_out);
+	const unsigned int lefthalf = rq->outputsize - righthalf;
 	unsigned char *src, *dst;
 
 	if (nrpages_out > 2) {
@@ -344,10 +345,10 @@ static int z_erofs_shifted_transform(struct z_erofs_decompress_req *rq,
 	if (nrpages_out == 2) {
 		DBG_BUGON(!rq->out[1]);
 		if (rq->out[1] == *rq->in) {
-			memmove(src, src + righthalf, rq->pageofs_out);
+			memmove(src, src + righthalf, lefthalf);
 		} else {
 			dst = kmap_atomic(rq->out[1]);
-			memcpy(dst, src + righthalf, rq->pageofs_out);
+			memcpy(dst, src + righthalf, lefthalf);
 			kunmap_atomic(dst);
 		}
 	}