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fs: allow AT_EMPTY_PATH in linkat(), limit that to CAP_DAC_READ_SEARCH 

We don't want to allow creation of private hardlinks by different application
using the fd passed to them via SCM_RIGHTS. So limit the null relative name
usage in linkat syscall to CAP_DAC_READ_SEARCH

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
This commit is contained in:
Aneesh Kumar K.V 2011-01-29 18:43:42 +05:30 committed by Al Viro
parent 326be7b484
commit 11a7b371b6
1 changed files with 16 additions and 4 deletions
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20
fs/namei.c
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@ -2945,15 +2945,27 @@ SYSCALL_DEFINE5(linkat, int, olddfd, const char __user *, oldname,
struct dentry *new_dentry;
struct nameidata nd;
struct path old_path;
int how = 0;
int error;
char *to;
if ((flags & ~AT_SYMLINK_FOLLOW) != 0)
if ((flags & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH)) != 0)
return -EINVAL;
/*
* To use null names we require CAP_DAC_READ_SEARCH
* This ensures that not everyone will be able to create
* handlink using the passed filedescriptor.
*/
if (flags & AT_EMPTY_PATH) {
if (!capable(CAP_DAC_READ_SEARCH))
return -ENOENT;
how = LOOKUP_EMPTY;
}
error = user_path_at(olddfd, oldname,
flags & AT_SYMLINK_FOLLOW ? LOOKUP_FOLLOW : 0,
&old_path);
if (flags & AT_SYMLINK_FOLLOW)
how |= LOOKUP_FOLLOW;
error = user_path_at(olddfd, oldname, how, &old_path);
if (error)
return error;