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bpf: Fix pos computation for bpf_iter seq_ops->start()

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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 <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200722195156.4029817-1-yhs@fb.com
This commit is contained in:
Yonghong Song 2020-07-22 12:51:56 -07:00 committed by Alexei Starovoitov
parent 86176a1821
commit 3f9969f2c0
2 changed files with 10 additions and 12 deletions
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14
kernel/bpf/map_iter.c
View File

@ -7,7 +7,7 @@
#include <linux/btf_ids.h> #include <linux/btf_ids.h>
struct bpf_iter_seq_map_info { struct bpf_iter_seq_map_info {
u32 mid; u32 map_id;
}; };
static void *bpf_map_seq_start(struct seq_file *seq, loff_t *pos) static void *bpf_map_seq_start(struct seq_file *seq, loff_t *pos)
@ -15,10 +15,11 @@ static void *bpf_map_seq_start(struct seq_file *seq, loff_t *pos)
struct bpf_iter_seq_map_info *info = seq->private; struct bpf_iter_seq_map_info *info = seq->private;
struct bpf_map *map; 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) if (!map)
return NULL; return NULL;
if (*pos == 0)
++*pos; ++*pos;
return map; return map;
} }
@ -26,16 +27,11 @@ static void *bpf_map_seq_start(struct seq_file *seq, loff_t *pos)
static void *bpf_map_seq_next(struct seq_file *seq, void *v, loff_t *pos) 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_iter_seq_map_info *info = seq->private;
struct bpf_map *map;
++*pos; ++*pos;
++info->mid; ++info->map_id;
bpf_map_put((struct bpf_map *)v); bpf_map_put((struct bpf_map *)v);
map = bpf_map_get_curr_or_next(&info->mid); return bpf_map_get_curr_or_next(&info->map_id);
if (!map)
return NULL;
return map;
} }
struct bpf_iter__bpf_map { struct bpf_iter__bpf_map {

2
kernel/bpf/task_iter.c
View File

@ -51,6 +51,7 @@ static void *task_seq_start(struct seq_file *seq, loff_t *pos)
if (!task) if (!task)
return NULL; return NULL;
if (*pos == 0)
++*pos; ++*pos;
return task; return task;
} }
@ -210,6 +211,7 @@ static void *task_file_seq_start(struct seq_file *seq, loff_t *pos)
return NULL; return NULL;
} }
if (*pos == 0)
++*pos; ++*pos;
info->task = task; info->task = task;
info->files = files; info->files = files;