On Fri, Jul 24, 2020 at 10:22:36PM -0700, Pascal Bouchareine wrote:
This command attaches a description to a file descriptor for
troubleshooting purposes. The free string is displayed in the
process fdinfo file for that fd /proc/pid/fdinfo/fd.
One intended usage is to allow processes to self-document sockets
for netstat and friends to report
quoted hunk ↗ jump to hunk
+static long fcntl_set_description(struct file *file, char __user *desc)
+{
+ char *d;
+
+ d = strndup_user(desc, MAX_FILE_DESC_SIZE);
This should be kmem accounted because allocation is persistent.
To make things more entertaining, strndup_user() doesn't have gfp_t argument.
quoted hunk ↗ jump to hunk
+ if (IS_ERR(d))
+ return PTR_ERR(d);
+
+ spin_lock(&file->f_lock);
+ kfree(file->f_description);
+ file->f_description = d;
+ spin_unlock(&file->f_lock);
Generally kfree under spinlock is not good idea.
You can replace the pointer and free without spinlock.
quoted hunk ↗ jump to hunk
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -980,6 +980,9 @@ struct file {
struct address_space *f_mapping;
errseq_t f_wb_err;
errseq_t f_sb_err; /* for syncfs */
+
+#define MAX_FILE_DESC_SIZE 256
+ char *f_description;
struct file is nicely aligned to 256 bytes on distro configs.
Will this break everything?
$ cat /sys/kernel/slab/filp/object_size