pipe: add proc_dopipe_max_size() to safely assign pipe_max_size
pipe_max_size is assigned directly via procfs sysctl:
static struct ctl_table fs_table[] = {
...
{
.procname = "pipe-max-size",
.data = &pipe_max_size,
.maxlen = sizeof(int),
.mode = 0644,
.proc_handler = &pipe_proc_fn,
.extra1 = &pipe_min_size,
},
...
int pipe_proc_fn(struct ctl_table *table, int write, void __user *buf,
size_t *lenp, loff_t *ppos)
{
...
ret = proc_dointvec_minmax(table, write, buf, lenp, ppos)
...
and then later rounded in-place a few statements later:
...
pipe_max_size = round_pipe_size(pipe_max_size);
...
This leaves a window of time between initial assignment and rounding
that may be visible to other threads. (For example, one thread sets a
non-rounded value to pipe_max_size while another reads its value.)
Similar reads of pipe_max_size are potentially racy:
pipe.c :: alloc_pipe_info()
pipe.c :: pipe_set_size()
Add a new proc_dopipe_max_size() that consolidates reading the new value
from the user buffer, verifying bounds, and calling round_pipe_size()
with a single assignment to pipe_max_size.
Link: http://lkml.kernel.org/r/1507658689-11669-4-git-send-email-joe.lawrence@redhat.com
Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
Reported-by: Mikulas Patocka <mpatocka@redhat.com>
Reviewed-by: Mikulas Patocka <mpatocka@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/pipe.c b/fs/pipe.c
index f0f4ab3..6d98566 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -1020,7 +1020,7 @@
* Currently we rely on the pipe array holding a power-of-2 number
* of pages. Returns 0 on error.
*/
-static inline unsigned int round_pipe_size(unsigned int size)
+unsigned int round_pipe_size(unsigned int size)
{
unsigned long nr_pages;
@@ -1125,25 +1125,13 @@
}
/*
- * This should work even if CONFIG_PROC_FS isn't set, as proc_dointvec_minmax
+ * This should work even if CONFIG_PROC_FS isn't set, as proc_dopipe_max_size
* will return an error.
*/
int pipe_proc_fn(struct ctl_table *table, int write, void __user *buf,
size_t *lenp, loff_t *ppos)
{
- unsigned int rounded_pipe_max_size;
- int ret;
-
- ret = proc_douintvec_minmax(table, write, buf, lenp, ppos);
- if (ret < 0 || !write)
- return ret;
-
- rounded_pipe_max_size = round_pipe_size(pipe_max_size);
- if (rounded_pipe_max_size == 0)
- return -EINVAL;
-
- pipe_max_size = rounded_pipe_max_size;
- return ret;
+ return proc_dopipe_max_size(table, write, buf, lenp, ppos);
}
/*