On 08/16/2016 01:10 PM, Michael Kerrisk (man-pages) wrote:
When changing a pipe's capacity with fcntl(F_SETPIPE_SZ), various
limits defined by /proc/sys/fs/pipe-* files are checked to see
if unprivileged users are exceeding limits on memory consumption.
[...]
---
fs/pipe.c | 25 +++++++++++++++++--------
1 file changed, 17 insertions(+), 8 deletions(-)
diff --git a/fs/pipe.c b/fs/pipe.c
index 4ebe6b2..a98ebca 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -1122,14 +1122,23 @@ long pipe_fcntl(struct file *file, unsigned int cmd, unsigned long arg)
if (!nr_pages)
goto out;
- if (!capable(CAP_SYS_RESOURCE) && size > pipe_max_size) {
- ret = -EPERM;
- goto out;
- } else if ((too_many_pipe_buffers_hard(pipe->user) ||
- too_many_pipe_buffers_soft(pipe->user)) &&
- !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN)) {
- ret = -EPERM;
- goto out;
+ /*
+ * If trying to increase the pipe capacity, check that an
+ * unprivileged user is not trying to exceed various limits.
+ * (Decreasing the pipe capacity is always permitted, even
+ * if the user is currently over a limit.)
+ */
+ if (nr_pages > pipe->buffers) {
+ if (!capable(CAP_SYS_RESOURCE) && size > pipe_max_size) {
+ ret = -EPERM;
+ goto out;
+ } else if ((too_many_pipe_buffers_hard(pipe->user) ||
+ too_many_pipe_buffers_soft(pipe->user)) &&
+ !capable(CAP_SYS_RESOURCE) &&
+ !capable(CAP_SYS_ADMIN)) {
+ ret = -EPERM;
+ goto out;
+ }
}
ret = pipe_set_size(pipe, nr_pages);
break;
FWIW: Reviewed-by: Vegard Nossum <vegard.nossum@xxxxxxxxxx>
Vegard
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