From: Gao Xiang <gaoxiang25@xxxxxxxxxx> commit 4d2024370d877f9ac8b98694bcff666da6a5d333 upstream. rq->out[1] should be valid before accessing. Otherwise, in very rare cases, out-of-bound dirty onstack rq->out[1] can equal to *in and lead to unintended memmove behavior. Link: https://lore.kernel.org/r/20200107022546.19432-1-gaoxiang25@xxxxxxxxxx Fixes: 7fc45dbc938a ("staging: erofs: introduce generic decompression backend") Cc: <stable@xxxxxxxxxxxxxxx> # 5.3+ Reviewed-by: Chao Yu <yuchao0@xxxxxxxxxx> Signed-off-by: Gao Xiang <gaoxiang25@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- fs/erofs/decompressor.c | 22 ++++++++++------------ 1 file changed, 10 insertions(+), 12 deletions(-) --- a/fs/erofs/decompressor.c +++ b/fs/erofs/decompressor.c @@ -306,24 +306,22 @@ static int z_erofs_shifted_transform(con } src = kmap_atomic(*rq->in); - if (!rq->out[0]) { - dst = NULL; - } else { + if (rq->out[0]) { dst = kmap_atomic(rq->out[0]); memcpy(dst + rq->pageofs_out, src, righthalf); + kunmap_atomic(dst); } - if (rq->out[1] == *rq->in) { - memmove(src, src + righthalf, rq->pageofs_out); - } else if (nrpages_out == 2) { - if (dst) - kunmap_atomic(dst); + if (nrpages_out == 2) { DBG_BUGON(!rq->out[1]); - dst = kmap_atomic(rq->out[1]); - memcpy(dst, src + righthalf, rq->pageofs_out); + if (rq->out[1] == *rq->in) { + memmove(src, src + righthalf, rq->pageofs_out); + } else { + dst = kmap_atomic(rq->out[1]); + memcpy(dst, src + righthalf, rq->pageofs_out); + kunmap_atomic(dst); + } } - if (dst) - kunmap_atomic(dst); kunmap_atomic(src); return 0; }
