Commit 905eeb2b authored by Tatsuyuki Ishi's avatar Tatsuyuki Ishi Committed by Gao Xiang
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erofs: impersonate the opener's credentials when accessing backing file 



Previously, file operations on a file-backed mount used the current
process' credentials to access the backing FD. Attempting to do so on
Android lead to SELinux denials, as ACL rules on the backing file (e.g.
/system/apex/foo.apex) is restricted to a small set of process.
Arguably, this error is redundant and leaking implementation details, as
access to files on a mount is already ACL'ed by path.

Instead, override to use the opener's cred when accessing the backing
file. This makes the behavior similar to a loop-backed mount, which
uses kworker cred when accessing the backing file and does not cause
SELinux denials.

Signed-off-by: default avatarTatsuyuki Ishi <ishitatsuyuki@google.com>
Reviewed-by: default avatarGao Xiang <hsiangkao@linux.alibaba.com>
Reviewed-by: default avatarHongbo Li <lihongbo22@huawei.com>
Link: https://lore.kernel.org/r/20250612-b4-erofs-impersonate-v1-1-8ea7d6f65171@google.com


Signed-off-by: default avatarGao Xiang <hsiangkao@linux.alibaba.com>
parent 19272b37

fs/erofs/fileio.c

+3 −0
Original line number Diff line number Diff line
@@ -47,6 +47,7 @@ static void erofs_fileio_ki_complete(struct kiocb *iocb, long ret) 


static void erofs_fileio_rq_submit(struct erofs_fileio_rq *rq)

{

	const struct cred *old_cred;

	struct iov_iter iter;

	int ret;
@@ -60,7 +61,9 @@ static void erofs_fileio_rq_submit(struct erofs_fileio_rq *rq) 
		rq->iocb.ki_flags = IOCB_DIRECT;

	iov_iter_bvec(&iter, ITER_DEST, rq->bvecs, rq->bio.bi_vcnt,

		      rq->bio.bi_iter.bi_size);

	old_cred = override_creds(rq->iocb.ki_filp->f_cred);

	ret = vfs_iocb_iter_read(rq->iocb.ki_filp, &rq->iocb, &iter);

	revert_creds(old_cred);

	if (ret != -EIOCBQUEUED)

		erofs_fileio_ki_complete(&rq->iocb, ret);

}