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UPSTREAM: erofs: impersonate the opener's credentials when accessing backing file

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

Bug: 428292438
Change-Id: I1c3f08326ae1e6ba0bcaac1f9afb336645f8b065
(cherry picked from commit 905eeb2b7c33adda23a966aeb811ab4cb9e62031)
Signed-off-by: Wang Shuai <wangshuai12@xiaomi.corp-partner.google.com>
This commit is contained in:
Tatsuyuki Ishi
2025-06-12 19:18:25 +09:00
committed by Sandeep Dhavale
parent 4d0200d0a9
commit c40c54e669
1 changed files with 3 additions and 0 deletions
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3
fs/erofs/fileio.c
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@@ -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);
}