aboutsummaryrefslogtreecommitdiff
path: root/fs/seq_file.c
diff options
context:
space:
mode:
authorEarl Chew <echew@ixiacom.com>2012-03-21 16:33:43 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2012-03-21 17:54:54 -0700
commit7904ac84244b59f536c2a5d1066a10f46df07b08 (patch)
tree82d9c44c26b52954884a70f1ae2b7fa78ea8e633 /fs/seq_file.c
parentdc716e96f5a467835e8121e1caaf25d66a901cb3 (diff)
downloadlinux-stericsson-7904ac84244b59f536c2a5d1066a10f46df07b08.tar.gz
seq_file: fix mishandling of consecutive pread() invocations.
The following program illustrates the problem: char buf[8192]; int fd = open("/proc/self/maps", O_RDONLY); n = pread(fd, buf, sizeof(buf), 0); printf("%d\n", n); /* lseek(fd, 0, SEEK_CUR); */ /* Uncomment to work around */ n = pread(fd, buf, sizeof(buf), 0); printf("%d\n", n); The second printf() prints zero, but uncommenting the lseek() corrects its behaviour. To fix, make seq_read() mirror seq_lseek() when processing changes in *ppos. Restore m->version first, then if required traverse and update read_pos on success. Addresses https://bugzilla.kernel.org/show_bug.cgi?id=11856 Signed-off-by: Earl Chew <echew@ixiacom.com> Cc: Alexey Dobriyan <adobriyan@gmail.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'fs/seq_file.c')
-rw-r--r--fs/seq_file.c28
1 files changed, 15 insertions, 13 deletions
diff --git a/fs/seq_file.c b/fs/seq_file.c
index 4023d6be939b..aa242dc99373 100644
--- a/fs/seq_file.c
+++ b/fs/seq_file.c
@@ -140,9 +140,21 @@ ssize_t seq_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
mutex_lock(&m->lock);
+ /*
+ * seq_file->op->..m_start/m_stop/m_next may do special actions
+ * or optimisations based on the file->f_version, so we want to
+ * pass the file->f_version to those methods.
+ *
+ * seq_file->version is just copy of f_version, and seq_file
+ * methods can treat it simply as file version.
+ * It is copied in first and copied out after all operations.
+ * It is convenient to have it as part of structure to avoid the
+ * need of passing another argument to all the seq_file methods.
+ */
+ m->version = file->f_version;
+
/* Don't assume *ppos is where we left it */
if (unlikely(*ppos != m->read_pos)) {
- m->read_pos = *ppos;
while ((err = traverse(m, *ppos)) == -EAGAIN)
;
if (err) {
@@ -152,21 +164,11 @@ ssize_t seq_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
m->index = 0;
m->count = 0;
goto Done;
+ } else {
+ m->read_pos = *ppos;
}
}
- /*
- * seq_file->op->..m_start/m_stop/m_next may do special actions
- * or optimisations based on the file->f_version, so we want to
- * pass the file->f_version to those methods.
- *
- * seq_file->version is just copy of f_version, and seq_file
- * methods can treat it simply as file version.
- * It is copied in first and copied out after all operations.
- * It is convenient to have it as part of structure to avoid the
- * need of passing another argument to all the seq_file methods.
- */
- m->version = file->f_version;
/* grab buffer if we didn't have one */
if (!m->buf) {
m->buf = kmalloc(m->size = PAGE_SIZE, GFP_KERNEL);