[PATCH] proc: return on proc_readdir error

[Richard Genoud <richard.genoud@gmail.com>]

commit f0c3b5093addc8bfe9fe3a5b01acb7ec7969eafa
"[readdir] convert procfs" introduced a bug on the listing of the proc
file-system.
The return value of proc_readdir() isn't tested anymore in the
proc_root_readdir function.

This lead to an "interesting" behaviour when we are using the getdents()
system call with a buffer too small:
Instead of failing, it returns the first entries of /proc (enough to
fill the given buffer), plus the PID directories.

This is not triggered on glibc (as getdents is called with a 32KB
buffer), but on uclibc, the buffer size is only 1KB, thus some proc
entries are missing.
(described more in details here: https://lkml.org/lkml/2013/8/12/288 )

Signed-off-by: Richard Genoud <richard.genoud@gmail.com>
---
[added Linus Torvalds and Andrew Morton in CC since Al Viro seems to be
on holidays and it's starting to getting late in the -rc cycles]

 fs/proc/root.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/proc/root.c b/fs/proc/root.c
index 229e366..e0a790d 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c
@@ -205,7 +205,9 @@ static struct dentry *proc_root_lookup(struct inode * dir, struct dentry * dentr
 static int proc_root_readdir(struct file *file, struct dir_context *ctx)
 {
 	if (ctx->pos < FIRST_PROCESS_ENTRY) {
-		proc_readdir(file, ctx);
+		int error = proc_readdir(file, ctx);
+		if (unlikely(error <= 0))
+			return error;
 		ctx->pos = FIRST_PROCESS_ENTRY;
 	}
 
-- 
1.7.10.4