[PATCH v5 1/5] libfs: Return ENOSPC when the directory offset range is exhausted

cel
2024-12-15T18:58:21Z

Testing shows that the EBUSY error return from mtree_alloc_cyclic()
leaks into user space. The ERRORS section of "man creat(2)" says:

> EBUSY O_EXCL was specified in flags and pathname refers
> to a block device that is in use by the system
> (e.g., it is mounted).

ENOSPC is closer to what applications expect in this situation.

Note that the normal range of simple directory offset values is
2..2^63, so hitting this error is going to be rare to impossible.

Fixes: 6faddda69f62 ("libfs: Add directory operations for stable offsets")
Cc: <stable@vger.kernel.org> # v6.9+
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Yang Erkun <yangerkun@huawei.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
fs/libfs.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/libfs.c b/fs/libfs.c
index 748ac5923154..f6d04c69f195 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -292,7 +292,9 @@ int simple_offset_add(struct offset_ctx *octx, struct dentry *dentry)

ret = mtree_alloc_cyclic(&octx->mt, &offset, dentry, DIR_OFFSET_MIN,
LONG_MAX, &octx->next_offset, GFP_KERNEL);
- if (ret < 0)
+ if (unlikely(ret == -EBUSY))
+ return -ENOSPC;
+ if (unlikely(ret < 0))
return ret;

offset_set(dentry, offset);
--
2.47.0