pipe: fix limit checking in pipe_set_size()

[cascardo/linux.git] / fs / pipe.c

diff --git a/fs/pipe.c b/fs/pipe.c
index b9422bc..dc5f4c0 100644 (file)
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -1027,6 +1027,7 @@ static long pipe_set_size(struct pipe_inode_info *pipe, unsigned long arg)
 {
        struct pipe_buffer *bufs;
        unsigned int size, nr_pages;
+       long ret = 0;
 
        size = round_pipe_size(arg);
        nr_pages = size >> PAGE_SHIFT;
@@ -1034,13 +1035,26 @@ static long pipe_set_size(struct pipe_inode_info *pipe, unsigned long arg)
        if (!nr_pages)
                return -EINVAL;
 
-       if (!capable(CAP_SYS_RESOURCE) && size > pipe_max_size)
+       /*
+        * If trying to increase the pipe capacity, check that an
+        * unprivileged user is not trying to exceed various limits
+        * (soft limit check here, hard limit check just below).
+        * Decreasing the pipe capacity is always permitted, even
+        * if the user is currently over a limit.
+        */
+       if (nr_pages > pipe->buffers &&
+                       size > pipe_max_size && !capable(CAP_SYS_RESOURCE))
                return -EPERM;
 
-       if ((too_many_pipe_buffers_hard(pipe->user) ||
-                       too_many_pipe_buffers_soft(pipe->user)) &&
-                       !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN))
-               return -EPERM;
+       account_pipe_buffers(pipe->user, pipe->buffers, nr_pages);
+
+       if (nr_pages > pipe->buffers &&
+                       (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_revert_acct;
+       }
 
        /*
         * We can shrink the pipe, if arg >= pipe->nrbufs. Since we don't
@@ -1048,13 +1062,17 @@ static long pipe_set_size(struct pipe_inode_info *pipe, unsigned long arg)
         * again like we would do for growing. If the pipe currently
         * contains more buffers than arg, then return busy.
         */
-       if (nr_pages < pipe->nrbufs)
-               return -EBUSY;
+       if (nr_pages < pipe->nrbufs) {
+               ret = -EBUSY;
+               goto out_revert_acct;
+       }
 
        bufs = kcalloc(nr_pages, sizeof(*bufs),
                       GFP_KERNEL_ACCOUNT | __GFP_NOWARN);
-       if (unlikely(!bufs))
-               return -ENOMEM;
+       if (unlikely(!bufs)) {
+               ret = -ENOMEM;
+               goto out_revert_acct;
+       }
 
        /*
         * The pipe array wraps around, so just start the new one at zero
@@ -1077,12 +1095,15 @@ static long pipe_set_size(struct pipe_inode_info *pipe, unsigned long arg)
                        memcpy(bufs + head, pipe->bufs, tail * sizeof(struct pipe_buffer));
        }
 
-       account_pipe_buffers(pipe->user, pipe->buffers, nr_pages);
        pipe->curbuf = 0;
        kfree(pipe->bufs);
        pipe->bufs = bufs;
        pipe->buffers = nr_pages;
        return nr_pages * PAGE_SIZE;
+
+out_revert_acct:
+       account_pipe_buffers(pipe->user, nr_pages, pipe->buffers);
+       return ret;
 }
 
 /*