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Subject[PATCH v2] proc: Use seq_read_iter for /proc/*/maps
Date
Since seq_read_iter looks mature enough to be used for /proc/<pid>/maps,
re-allow applications to perform zero-copy data forwarding from it.

Some executable-inspecting tools rely on patching entry point
instructions with minimal machine code that uses sendfile to read
/proc/self/maps to stdout. The sendfile call allows them to do it
faster and without excessive allocations.

This is inspired by the series by Cristoph Hellwig (linked).

Changes since v1:

only change proc_pid_maps_operations

Link: https://lore.kernel.org/lkml/20201104082738.1054792-1-hch@lst.de/
Fixes: 36e2c7421f02 ("fs: don't allow splice read/write without explicit ops")
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Arkadiusz Kozdra (Arusekk) <arek_koz@o2.pl>
---
fs/proc/task_mmu.c | 3 ++-
fs/proc/task_nommu.c | 3 ++-
2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index e862cab69583..06282294ddb8 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -351,7 +351,8 @@ static int pid_maps_open(struct inode *inode, struct file *file)

const struct file_operations proc_pid_maps_operations = {
.open = pid_maps_open,
- .read = seq_read,
+ .read_iter = seq_read_iter,
+ .splice_read = generic_file_splice_read,
.llseek = seq_lseek,
.release = proc_map_release,
};
diff --git a/fs/proc/task_nommu.c b/fs/proc/task_nommu.c
index a6d21fc0033c..e55e79fd0175 100644
--- a/fs/proc/task_nommu.c
+++ b/fs/proc/task_nommu.c
@@ -295,7 +295,8 @@ static int pid_maps_open(struct inode *inode, struct file *file)

const struct file_operations proc_pid_maps_operations = {
.open = pid_maps_open,
- .read = seq_read,
+ .read_iter = seq_read_iter,
+ .splice_read = generic_file_splice_read,
.llseek = seq_lseek,
.release = map_release,
};
--
2.31.1
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