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Message-ID: <20080413084843.GA7227@martell.zuzino.mipt.ru>
Date: Sun, 13 Apr 2008 12:48:43 +0400
From: Alexey Dobriyan <adobriyan@...il.com>
To: akpm@...l.org, mchehab@...radead.org
Cc: linux-kernel@...r.kernel.org, v4l-dvb-maintainer@...uxtv.org
Subject: [PATCH] Fix concurrent read from /proc/videocodecs
Observation one: ->write_proc and ->data assignments aren't needed. Removed.
Observation two: codecs lists are unprotected. Patch doesn't fix this.
Observation three:
/proc/videocodecs printout is done to temporary _global_ buffer which
is freed in between. Consequently, two users hitting this file can
screwup each other.
Steps to reproduce:
modprobe videocodec
while true; do cat /proc/videocodecs &>/dev/null; done &
while true; do cat /proc/videocodecs &>/dev/null; done &
The fix is switching to seq_files, this removes code, especially some
line-length "logic".
Signed-off-by: Alexey Dobriyan <adobriyan@...il.com>
---
Tested on empty file, I don't have hardware.
drivers/media/video/videocodec.c | 113 ++++++---------------------------------
1 file changed, 19 insertions(+), 94 deletions(-)
--- a/drivers/media/video/videocodec.c
+++ b/drivers/media/video/videocodec.c
@@ -39,6 +39,7 @@
#ifdef CONFIG_PROC_FS
#include <linux/proc_fs.h>
+#include <linux/seq_file.h>
#include <asm/uaccess.h>
#endif
@@ -320,56 +321,22 @@ videocodec_unregister (const struct videocodec *codec)
}
#ifdef CONFIG_PROC_FS
-/* ============ */
-/* procfs stuff */
-/* ============ */
-
-static char *videocodec_buf = NULL;
-static int videocodec_bufsize;
-
-static int
-videocodec_build_table (void)
+static int proc_videocodecs_show(struct seq_file *m, void *v)
{
struct codec_list *h = codeclist_top;
struct attached_list *a;
- int i = 0, size;
-
- // sum up amount of slaves plus their attached masters
- while (h) {
- i += h->attached + 1;
- h = h->next;
- }
-#define LINESIZE 100
- size = LINESIZE * (i + 1);
- dprintk(3, "videocodec_build table: %d entries, %d bytes\n", i,
- size);
-
- kfree(videocodec_buf);
- videocodec_buf = kmalloc(size, GFP_KERNEL);
-
- if (!videocodec_buf)
- return 0;
-
- i = 0;
- i += scnprintf(videocodec_buf + i, size - 1,
- "<S>lave or attached <M>aster name type flags magic ");
- i += scnprintf(videocodec_buf + i, size -i - 1, "(connected as)\n");
+ seq_printf(m, "<S>lave or attached <M>aster name type flags magic ");
+ seq_printf(m, "(connected as)\n");
h = codeclist_top;
while (h) {
- if (i > (size - LINESIZE))
- break; // security check
- i += scnprintf(videocodec_buf + i, size -i -1,
- "S %32s %04x %08lx %08lx (TEMPLATE)\n",
+ seq_printf(m, "S %32s %04x %08lx %08lx (TEMPLATE)\n",
h->codec->name, h->codec->type,
h->codec->flags, h->codec->magic);
a = h->list;
while (a) {
- if (i > (size - LINESIZE))
- break; // security check
- i += scnprintf(videocodec_buf + i, size -i -1,
- "M %32s %04x %08lx %08lx (%s)\n",
+ seq_printf(m, "M %32s %04x %08lx %08lx (%s)\n",
a->codec->master_data->name,
a->codec->master_data->type,
a->codec->master_data->flags,
@@ -380,54 +347,21 @@ videocodec_build_table (void)
h = h->next;
}
- return i;
+ return 0;
}
-//The definition:
-//typedef int (read_proc_t)(char *page, char **start, off_t off,
-// int count, int *eof, void *data);
-
-static int
-videocodec_info (char *buffer,
- char **buffer_location,
- off_t offset,
- int buffer_length,
- int *eof,
- void *data)
+static int proc_videocodecs_open(struct inode *inode, struct file *file)
{
- int size;
-
- dprintk(3, "videocodec_info: offset: %ld, len %d / size %d\n",
- offset, buffer_length, videocodec_bufsize);
-
- if (offset == 0) {
- videocodec_bufsize = videocodec_build_table();
- }
- if ((offset < 0) || (offset >= videocodec_bufsize)) {
- dprintk(4,
- "videocodec_info: call delivers no result, return 0\n");
- *eof = 1;
- return 0;
- }
-
- if (buffer_length < (videocodec_bufsize - offset)) {
- dprintk(4, "videocodec_info: %ld needed, %d got\n",
- videocodec_bufsize - offset, buffer_length);
- size = buffer_length;
- } else {
- dprintk(4, "videocodec_info: last reading of %ld bytes\n",
- videocodec_bufsize - offset);
- size = videocodec_bufsize - offset;
- *eof = 1;
- }
-
- memcpy(buffer, videocodec_buf + offset, size);
- /* doesn't work... */
- /* copy_to_user(buffer, videocodec_buf+offset, size); */
- /* *buffer_location = videocodec_buf+offset; */
-
- return size;
+ return single_open(file, proc_videocodecs_show, NULL);
}
+
+static const struct file_operations videocodecs_proc_fops = {
+ .owner = THIS_MODULE,
+ .open = proc_videocodecs_open,
+ .read = seq_read,
+ .llseek = seq_lseek,
+ .release = single_release,
+};
#endif
/* ===================== */
@@ -444,16 +378,8 @@ videocodec_init (void)
VIDEOCODEC_VERSION);
#ifdef CONFIG_PROC_FS
- videocodec_buf = NULL;
- videocodec_bufsize = 0;
-
- videocodec_proc_entry = create_proc_entry("videocodecs", 0, NULL);
- if (videocodec_proc_entry) {
- videocodec_proc_entry->read_proc = videocodec_info;
- videocodec_proc_entry->write_proc = NULL;
- videocodec_proc_entry->data = NULL;
- videocodec_proc_entry->owner = THIS_MODULE;
- } else {
+ videocodec_proc_entry = proc_create("videocodecs", 0, NULL, &videocodecs_proc_fops);
+ if (!videocodec_proc_entry) {
dprintk(1, KERN_ERR "videocodec: can't init procfs.\n");
}
#endif
@@ -465,7 +391,6 @@ videocodec_exit (void)
{
#ifdef CONFIG_PROC_FS
remove_proc_entry("videocodecs", NULL);
- kfree(videocodec_buf);
#endif
}
--
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