bpf: Fix pos computation for bpf_iter seq_ops->start() (3f9969f2) · Commits · 戴 / test

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: ("bpf: Add bpf_map iterator") Fixes: ("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

kernel/bpf/map_iter.c

+6 −10

Original line number	Diff line number	Diff line
		@@ -7,7 +7,7 @@
		#include <linux/btf_ids.h>

		struct bpf_iter_seq_map_info {
		u32 mid;
		u32 map_id;
		};

		static void bpf_map_seq_start(struct seq_file seq, loff_t *pos)
		@@ -15,10 +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_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;

		if (*pos == 0)
		++*pos;
		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)
		{
		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 {

kernel/bpf/task_iter.c

+4 −2

Original line number	Diff line number	Diff line
		@@ -51,6 +51,7 @@ static void task_seq_start(struct seq_file seq, loff_t *pos)
		if (!task)
		return NULL;

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

		if (*pos == 0)
		++*pos;
		info->task = task;
		info->files = files;

Admin message