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Date: Sun, 23 Jan 2022 22:23:33 +0800 From: Hao Lee <haolee.swjtu@...il.com> To: Alexey Dobriyan <adobriyan@...il.com> Cc: Andrew Morton <akpm@...ux-foundation.org>, christian.brauner@...ntu.com, Kees Cook <keescook@...omium.org>, jamorris@...ux.microsoft.com, linux-fsdevel@...r.kernel.org, LKML <linux-kernel@...r.kernel.org> Subject: Re: [PATCH v2] proc: alloc PATH_MAX bytes for /proc/${pid}/fd/ symlinks On Sun, Jan 23, 2022 at 9:58 PM Alexey Dobriyan <adobriyan@...il.com> wrote: > > From: Hao Lee <haolee.swjtu@...il.com> > > 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. This is indeed a worthy addition. Thanks. Regards, Hao Lee > An unlinked file > with very long canonical pathname will readlink differently > because "(deleted)" eats into a buffer. --adobriyan > > Signed-off-by: Hao Lee <haolee.swjtu@...il.com> > Signed-off-by: Alexey Dobriyan <adobriyan@...il.com> > --- > > fs/proc/base.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > --- a/fs/proc/base.c > +++ b/fs/proc/base.c > @@ -1764,25 +1764,25 @@ static const char *proc_pid_get_link(struct dentry *dentry, > > static int do_proc_readlink(struct path *path, char __user *buffer, int buflen) > { > - char *tmp = (char *)__get_free_page(GFP_KERNEL); > + char *tmp = (char *)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; > } >
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