diff options
| -rw-r--r-- | Documentation/sysctl/fs.txt | 36 | ||||
| -rw-r--r-- | fs/namei.c | 53 | ||||
| -rw-r--r-- | include/linux/fs.h | 2 | ||||
| -rw-r--r-- | kernel/sysctl.c | 18 |
4 files changed, 106 insertions, 3 deletions
diff --git a/Documentation/sysctl/fs.txt b/Documentation/sysctl/fs.txt index 35e17f748ca7..af5859b2d0f9 100644 --- a/Documentation/sysctl/fs.txt +++ b/Documentation/sysctl/fs.txt @@ -34,7 +34,9 @@ Currently, these files are in /proc/sys/fs: - overflowgid - pipe-user-pages-hard - pipe-user-pages-soft +- protected_fifos - protected_hardlinks +- protected_regular - protected_symlinks - suid_dumpable - super-max @@ -182,6 +184,24 @@ applied. ============================================================== +protected_fifos: + +The intent of this protection is to avoid unintentional writes to +an attacker-controlled FIFO, where a program expected to create a regular +file. + +When set to "0", writing to FIFOs is unrestricted. + +When set to "1" don't allow O_CREAT open on FIFOs that we don't own +in world writable sticky directories, unless they are owned by the +owner of the directory. + +When set to "2" it also applies to group writable sticky directories. + +This protection is based on the restrictions in Openwall. + +============================================================== + protected_hardlinks: A long-standing class of security issues is the hardlink-based @@ -202,6 +222,22 @@ This protection is based on the restrictions in Openwall and grsecurity. ============================================================== +protected_regular: + +This protection is similar to protected_fifos, but it +avoids writes to an attacker-controlled regular file, where a program +expected to create one. + +When set to "0", writing to regular files is unrestricted. + +When set to "1" don't allow O_CREAT open on regular files that we +don't own in world writable sticky directories, unless they are +owned by the owner of the directory. + +When set to "2" it also applies to group writable sticky directories. + +============================================================== + protected_symlinks: A long-standing class of security issues is the symlink-based diff --git a/fs/namei.c b/fs/namei.c index 85ac38b99065..eb4626bad88a 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -892,6 +892,8 @@ static inline void put_link(struct nameidata *nd) int sysctl_protected_symlinks __read_mostly = 0; int sysctl_protected_hardlinks __read_mostly = 0; +int sysctl_protected_fifos __read_mostly; +int sysctl_protected_regular __read_mostly; /** * may_follow_link - Check symlink following for unsafe situations @@ -1005,6 +1007,45 @@ static int may_linkat(struct path *link) return -EPERM; } +/** + * may_create_in_sticky - Check whether an O_CREAT open in a sticky directory + * should be allowed, or not, on files that already + * exist. + * @dir: the sticky parent directory + * @inode: the inode of the file to open + * + * Block an O_CREAT open of a FIFO (or a regular file) when: + * - sysctl_protected_fifos (or sysctl_protected_regular) is enabled + * - the file already exists + * - we are in a sticky directory + * - we don't own the file + * - the owner of the directory doesn't own the file + * - the directory is world writable + * If the sysctl_protected_fifos (or sysctl_protected_regular) is set to 2 + * the directory doesn't have to be world writable: being group writable will + * be enough. + * + * Returns 0 if the open is allowed, -ve on error. + */ +static int may_create_in_sticky(struct dentry * const dir, + struct inode * const inode) +{ + if ((!sysctl_protected_fifos && S_ISFIFO(inode->i_mode)) || + (!sysctl_protected_regular && S_ISREG(inode->i_mode)) || + likely(!(dir->d_inode->i_mode & S_ISVTX)) || + uid_eq(inode->i_uid, dir->d_inode->i_uid) || + uid_eq(current_fsuid(), inode->i_uid)) + return 0; + + if (likely(dir->d_inode->i_mode & 0002) || + (dir->d_inode->i_mode & 0020 && + ((sysctl_protected_fifos >= 2 && S_ISFIFO(inode->i_mode)) || + (sysctl_protected_regular >= 2 && S_ISREG(inode->i_mode))))) { + return -EACCES; + } + return 0; +} + static __always_inline const char *get_link(struct nameidata *nd) { @@ -3356,9 +3397,15 @@ finish_open: if (error) return error; audit_inode(nd->name, nd->path.dentry, 0); - error = -EISDIR; - if ((open_flag & O_CREAT) && d_is_dir(nd->path.dentry)) - goto out; + if (open_flag & O_CREAT) { + error = -EISDIR; + if (d_is_dir(nd->path.dentry)) + goto out; + error = may_create_in_sticky(dir, + d_backing_inode(nd->path.dentry)); + if (unlikely(error)) + goto out; + } error = -ENOTDIR; if ((nd->flags & LOOKUP_DIRECTORY) && !d_can_lookup(nd->path.dentry)) goto out; diff --git a/include/linux/fs.h b/include/linux/fs.h index e9867aff53d8..bcad2b963296 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -69,6 +69,8 @@ extern struct inodes_stat_t inodes_stat; extern int leases_enable, lease_break_time; extern int sysctl_protected_symlinks; extern int sysctl_protected_hardlinks; +extern int sysctl_protected_fifos; +extern int sysctl_protected_regular; struct buffer_head; typedef int (get_block_t)(struct inode *inode, sector_t iblock, diff --git a/kernel/sysctl.c b/kernel/sysctl.c index 7df6be31be36..23f658d311c0 100644 --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -1795,6 +1795,24 @@ static struct ctl_table fs_table[] = { .extra2 = &one, }, { + .procname = "protected_fifos", + .data = &sysctl_protected_fifos, + .maxlen = sizeof(int), + .mode = 0600, + .proc_handler = proc_dointvec_minmax, + .extra1 = &zero, + .extra2 = &two, + }, + { + .procname = "protected_regular", + .data = &sysctl_protected_regular, + .maxlen = sizeof(int), + .mode = 0600, + .proc_handler = proc_dointvec_minmax, + .extra1 = &zero, + .extra2 = &two, + }, + { .procname = "suid_dumpable", .data = &suid_dumpable, .maxlen = sizeof(int), |