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    Subject[PATCH 5.18 480/879] erofs: fix buffer copy overflow of ztailpacking feature
    Date
    From: Gao Xiang <hsiangkao@linux.alibaba.com>

    [ 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@coolpad.com>
    Reviewed-by: Chao Yu <chao@kernel.org>
    Link: https://lore.kernel.org/r/20220512115833.24175-1-hsiangkao@linux.alibaba.com
    Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    fs/erofs/decompressor.c | 5 +++--
    1 file changed, 3 insertions(+), 2 deletions(-)

    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);
    }
    }
    --
    2.35.1


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