Messages in this thread Patch in this message | | | From | John Keeping <> | Subject | [PATCH] net/core: Fix seeking in /proc/net/dev | Date | Fri, 6 Apr 2012 18:05:44 +0100 |
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Commit f04565ddf52e4 (dev: use name hash for dev_seq_ops) introduced code that fails to check the requested position when getting an item for /proc/net/dev. This means that any code which seeks within this file is likely to receive corrupted data.
A test case for this is to use the read builtin in bash:
$ while read line; do echo "$line"; done </proc/net/dev | cut -c-20 Inter-| Receive face |bytes packe virbr0: 20706 0 lo: 2329335 10305 eth0: 0
compared to just cat'ing the file:
$ cat /proc/net/dev | cut -c-20 Inter-| Receive face |bytes pack lo: 2329335 10 virbr0: 20706 sit0: 0 wlan0: 1727234745 1 eth0: 0
This patch takes the sledgehammer approach of starting again from the beginning if asked to seek backwards.
Signed-off-by: John Keeping <john@keeping.me.uk>
--- I have made the minimal change required to fix the bug here. If desired I can spend some more time and enhance the dev_from_new_bucket and dev_from_same_bucket functions to support walking backwards as well as forwards through the items in the table.
--- net/core/dev.c | 24 +++++++++++++++++++----- 1 files changed, 19 insertions(+), 5 deletions(-)
diff --git a/net/core/dev.c b/net/core/dev.c index 6ca32f6..66b1e891 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -4040,6 +4040,7 @@ static int dev_ifconf(struct net *net, char __user *arg) struct dev_iter_state { struct seq_net_private p; + loff_t expected_pos; /* current index */ unsigned int pos; /* bucket << BUCKET_SPACE + offset */ }; @@ -4096,24 +4097,37 @@ static inline struct net_device *dev_from_new_bucket(struct seq_file *seq) void *dev_seq_start(struct seq_file *seq, loff_t *pos) __acquires(RCU) { + struct net_device *dev; struct dev_iter_state *state = seq->private; rcu_read_lock(); - if (!*pos) + if (!*pos) { + state->expected_pos = 0; + state->pos = 0; return SEQ_START_TOKEN; + } - /* check for end of the hash */ - if (state->pos == 0 && *pos > 1) - return NULL; + /* If we're asked for something behind where we are, start again. */ + if (state->expected_pos >= *pos) { + state->expected_pos = 0; + state->pos = 0; + } - return dev_from_new_bucket(seq); + do { + dev = dev_from_new_bucket(seq); + ++state->expected_pos; + } while (dev && state->expected_pos < *pos); + + return dev; } void *dev_seq_next(struct seq_file *seq, void *v, loff_t *pos) { struct net_device *dev; + struct dev_iter_state *state = seq->private; ++*pos; + state->expected_pos = *pos; if (v == SEQ_START_TOKEN) return dev_from_new_bucket(seq); -- 1.7.8.5
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