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proc: alloc PATH_MAX bytes for /proc/${pid}/fd/ symlinks

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It's not a standard approach that use __get_free_page() to alloc path
buffer directly.  We'd better use kmalloc and PATH_MAX.

	PAGE_SIZE is different on different archs. An unlinked file
	with very long canonical pathname will readlink differently
	because "(deleted)" eats into a buffer.	--adobriyan

[akpm@linux-foundation.org: remove now-unneeded cast]

Link: https://lkml.kernel.org/r/Ye1fCxyZZ0I5lgOL@localhost.localdomain
Signed-off-by: Hao Lee <haolee.swjtu@gmail.com>
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Christian Brauner <christian.brauner@ubuntu.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: James Morris <jamorris@linux.microsoft.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Hao Lee 2022-03-23 16:05:20 -07:00 committed by Linus Torvalds
parent f443e374ae
commit 3a72917ccf
1 changed files with 4 additions and 4 deletions
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8
fs/proc/base.c
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@ -1764,25 +1764,25 @@ out:
static int do_proc_readlink(struct path *path, char __user *buffer, int buflen)
{
char *tmp = (char *)__get_free_page(GFP_KERNEL);
char *tmp = kmalloc(PATH_MAX, GFP_KERNEL);
char *pathname;
int len;
if (!tmp)
return -ENOMEM;
pathname = d_path(path, tmp, PAGE_SIZE);
pathname = d_path(path, tmp, PATH_MAX);
len = PTR_ERR(pathname);
if (IS_ERR(pathname))
goto out;
len = tmp + PAGE_SIZE - 1 - pathname;
len = tmp + PATH_MAX - 1 - pathname;
if (len > buflen)
len = buflen;
if (copy_to_user(buffer, pathname, len))
len = -EFAULT;
out:
free_page((unsigned long)tmp);
kfree(tmp);
return len;
}