libfs: Return ENOSPC when the directory offset range is exhausted

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>
Link: https://lore.kernel.org/r/20241228175522.1854234-2-cel@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/fs/libfs.c b/fs/libfs.c
index 748ac59231547c29abcbade3fa025e3b00533d8b..3da58a92f48fe22a8e177b16f1518d718ed92497 100644 (file)
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -292,8 +292,8 @@ 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)
-               return ret;
+       if (unlikely(ret < 0))
+               return ret == -EBUSY ? -ENOSPC : ret;
 
        offset_set(dentry, offset);
        return 0;