From 3f9969f2c040ba2ba635b6b5a7051f404bcc634d Mon Sep 17 00:00:00 2001 From: Yonghong Song Date: Wed, 22 Jul 2020 12:51:56 -0700 Subject: [PATCH] bpf: Fix pos computation for bpf_iter seq_ops->start() Currently, the pos pointer in bpf iterator map/task/task_file seq_ops->start() is always incremented. This is incorrect. It should be increased only if *pos is 0 (for SEQ_START_TOKEN) since these start() function actually returns the first real object. If *pos is not 0, it merely found the object based on the state in seq->private, and not really advancing the *pos. This patch fixed this issue by only incrementing *pos if it is 0. Note that the old *pos calculation, although not correct, does not affect correctness of bpf_iter as bpf_iter seq_file->read() does not support llseek. This patch also renamed "mid" in bpf_map iterator seq_file private data to "map_id" for better clarity. Fixes: 6086d29def80 ("bpf: Add bpf_map iterator") Fixes: eaaacd23910f ("bpf: Add task and task/file iterator targets") Signed-off-by: Yonghong Song Signed-off-by: Alexei Starovoitov Link: https://lore.kernel.org/bpf/20200722195156.4029817-1-yhs@fb.com --- kernel/bpf/map_iter.c | 16 ++++++---------- kernel/bpf/task_iter.c | 6 ++++-- 2 files changed, 10 insertions(+), 12 deletions(-) diff --git a/kernel/bpf/map_iter.c b/kernel/bpf/map_iter.c index 8a7af11b411f..5926c76d854e 100644 --- a/kernel/bpf/map_iter.c +++ b/kernel/bpf/map_iter.c @@ -7,7 +7,7 @@ #include struct bpf_iter_seq_map_info { - u32 mid; + u32 map_id; }; static void *bpf_map_seq_start(struct seq_file *seq, loff_t *pos) @@ -15,27 +15,23 @@ static void *bpf_map_seq_start(struct seq_file *seq, loff_t *pos) struct bpf_iter_seq_map_info *info = seq->private; struct bpf_map *map; - map = bpf_map_get_curr_or_next(&info->mid); + map = bpf_map_get_curr_or_next(&info->map_id); if (!map) return NULL; - ++*pos; + if (*pos == 0) + ++*pos; return map; } static void *bpf_map_seq_next(struct seq_file *seq, void *v, loff_t *pos) { struct bpf_iter_seq_map_info *info = seq->private; - struct bpf_map *map; ++*pos; - ++info->mid; + ++info->map_id; bpf_map_put((struct bpf_map *)v); - map = bpf_map_get_curr_or_next(&info->mid); - if (!map) - return NULL; - - return map; + return bpf_map_get_curr_or_next(&info->map_id); } struct bpf_iter__bpf_map { diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c index 2feecf095609..1039e52ebd8b 100644 --- a/kernel/bpf/task_iter.c +++ b/kernel/bpf/task_iter.c @@ -51,7 +51,8 @@ static void *task_seq_start(struct seq_file *seq, loff_t *pos) if (!task) return NULL; - ++*pos; + if (*pos == 0) + ++*pos; return task; } @@ -210,7 +211,8 @@ static void *task_file_seq_start(struct seq_file *seq, loff_t *pos) return NULL; } - ++*pos; + if (*pos == 0) + ++*pos; info->task = task; info->files = files;