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sysfs: clamp show() return value in sysfs_kf_read()

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sysfs_kf_seq_show() defends against buggy show() callbacks that return
larger than PAGE_SIZE by clamping the value and printing a warning.
sysfs_kf_read(), the prealloc variant, has no such defense.

The only current in-tree user of __ATTR_PREALLOC is drivers/md/md.c,
whose show() callbacks are well-behaved, so this is hardening against
future drivers doing foolish things and out-of-tree code doing even more
foolish things.

Cc: NeilBrown <neil@brown.name>
Cc: Tejun Heo <tj@kernel.org>
Fixes: 2b75869bba ("sysfs/kernfs: allow attributes to request write buffer be pre-allocated.")
Assisted-by: gregkh_clanker_t1000
Reviewed-by: Rafael J. Wysocki (Intel) <rafael@kernel.org>
Reviewed-by: Danilo Krummrich <dakr@kernel.org>
Link: https://patch.msgid.link/2026052000-drove-unicycle-d61b@gregkh
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Greg Kroah-Hartman
2026-05-20 15:07:01 +02:00
parent 8d3bea93f4
commit 454257f6d1
1 changed files with 4 additions and 0 deletions
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4
fs/sysfs/file.c
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@@ -119,6 +119,10 @@ static ssize_t sysfs_kf_read(struct kernfs_open_file *of, char *buf,
len = ops->show(kobj, of->kn->priv, buf);
if (len < 0)
return len;
if (len >= (ssize_t)PAGE_SIZE) {
printk("fill_read_buffer: %pS returned bad count\n", ops->show);
len = PAGE_SIZE - 1;
}
if (pos) {
if (len <= pos)
return 0;