[PATCH] Allowing user processes to rise their oom_adj value

[Guillem Jover <guillem.jover@nokia.com>]

Currently a user process cannot rise its own oom_adj value (i.e.
unprotecting itself from the OOM killer). As this value is stored
in the task structure it gets inherited and the unprivileged childs
will be unable to rise it.

The EPERM will be handled by the generic proc fs layer, as only
processes with the proper caps or the owner of the process will be
able to write to the file. So we allow only the processes with
CAP_SYS_RESOURCE to lower the value, otherwise it will get an EACCES
which seems more appropriate than EPERM.

Signed-off-by: Guillem Jover <guillem.jover@nokia.com>
---
 fs/proc/base.c |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 8df2740..955bb0a 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -682,8 +682,6 @@ static ssize_t oom_adjust_write(struct f
 	char buffer[PROC_NUMBUF], *end;
 	int oom_adjust;
 
-	if (!capable(CAP_SYS_RESOURCE))
-		return -EPERM;
 	memset(buffer, 0, sizeof(buffer));
 	if (count > sizeof(buffer) - 1)
 		count = sizeof(buffer) - 1;
@@ -698,6 +696,10 @@ static ssize_t oom_adjust_write(struct f
 	task = get_proc_task(file->f_dentry->d_inode);
 	if (!task)
 		return -ESRCH;
+	if (oom_adjust < task->oomkilladj && !capable(CAP_SYS_RESOURCE)) {
+		put_task_struct(task);
+		return -EACCES;
+	}
 	task->oomkilladj = oom_adjust;
 	put_task_struct(task);
 	if (end - buffer == 0)
-- 
1.4.3.3