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authorLinus Torvalds <torvalds@linux-foundation.org>2012-09-21 11:48:05 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2012-09-21 11:48:05 -0700
commite05e279e6fc940a2adb9d4d4bf2b814dfc286176 (patch)
tree2dfeef2f02576933e752d1fb40e21d810e224a58 /fs/debugfs/file.c
parent36048853c5257a7b6df346b83758ffa776a59e9f (diff)
debugfs: fix u32_array race in format_array_alloc
The format_array_alloc() function is fundamentally racy, in that it prints the array twice: once to figure out how much space to allocate for the buffer, and the second time to actually print out the data. If any of the array contents changes in between, the allocation size may be wrong, and the end result may be truncated in odd ways. Just don't do it. Allocate a maximum-sized array up-front, and just format the array contents once. The only user of the u32_array interfaces is the Xen spinlock statistics code, and it has 31 entries in the arrays, so the maximum size really isn't that big, and the end result is much simpler code without the bug. Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'fs/debugfs/file.c')
-rw-r--r--fs/debugfs/file.c57
1 files changed, 23 insertions, 34 deletions
diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
index a09d3c0aad6..c5ca6ae5a30 100644
--- a/fs/debugfs/file.c
+++ b/fs/debugfs/file.c
@@ -526,55 +526,44 @@ struct array_data {
u32 elements;
};
-static size_t format_array(char *buf, size_t bufsize, const char *fmt,
- u32 *array, u32 array_size)
+static size_t u32_format_array(char *buf, size_t bufsize,
+ u32 *array, int array_size)
{
size_t ret = 0;
- u32 i;
- for (i = 0; i < array_size; i++) {
+ while (--array_size >= 0) {
size_t len;
+ char term = array_size ? ' ' : '\n';
- len = snprintf(buf, bufsize, fmt, array[i]);
- len++; /* ' ' or '\n' */
+ len = snprintf(buf, bufsize, "%u%c", *array++, term);
ret += len;
- if (buf) {
- buf += len;
- bufsize -= len;
- buf[-1] = (i == array_size-1) ? '\n' : ' ';
- }
+ buf += len;
+ bufsize -= len;
}
-
- ret++; /* \0 */
- if (buf)
- *buf = '\0';
-
- return ret;
-}
-
-static char *format_array_alloc(const char *fmt, u32 *array,
- u32 array_size)
-{
- size_t len = format_array(NULL, 0, fmt, array, array_size);
- char *ret;
-
- ret = kmalloc(len, GFP_KERNEL);
- if (ret == NULL)
- return NULL;
-
- format_array(ret, len, fmt, array, array_size);
return ret;
}
static int u32_array_open(struct inode *inode, struct file *file)
{
struct array_data *data = inode->i_private;
-
- file->private_data = format_array_alloc("%u", data->array,
- data->elements);
- if (!file->private_data)
+ int size, elements = data->elements;
+ char *buf;
+
+ /*
+ * Max size:
+ * - 10 digits + ' '/'\n' = 11 bytes per number
+ * - terminating NUL character
+ */
+ size = elements*11;
+ buf = kmalloc(size+1, GFP_KERNEL);
+ if (!buf)
return -ENOMEM;
+ buf[size] = 0;
+
+ file->private_data = buf;
+ u32_format_array(buf, size, data->array, data->elements);
+
return nonseekable_open(inode, file);
}