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authorLinus Torvalds <torvalds@linux-foundation.org>2018-07-03 17:10:19 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2018-07-05 12:36:36 -0700
commit0fa3ecd87848c9c93c2c828ef4c3a8ca36ce46c7 (patch)
tree380bffd5014564f906357aaf5255e81b7c466353
parentd02d21ea007b6b33cdaf15c2f84fb1fea996ecc2 (diff)
Fix up non-directory creation in SGID directories
sgid directories have special semantics, making newly created files in the directory belong to the group of the directory, and newly created subdirectories will also become sgid. This is historically used for group-shared directories. But group directories writable by non-group members should not imply that such non-group members can magically join the group, so make sure to clear the sgid bit on non-directories for non-members (but remember that sgid without group execute means "mandatory locking", just to confuse things even more). Reported-by: Jann Horn <jannh@google.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--fs/inode.c6
1 files changed, 6 insertions, 0 deletions
diff --git a/fs/inode.c b/fs/inode.c
index 2c300e981796..8c86c809ca17 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -1999,8 +1999,14 @@ void inode_init_owner(struct inode *inode, const struct inode *dir,
inode->i_uid = current_fsuid();
if (dir && dir->i_mode & S_ISGID) {
inode->i_gid = dir->i_gid;
+
+ /* Directories are special, and always inherit S_ISGID */
if (S_ISDIR(mode))
mode |= S_ISGID;
+ else if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP) &&
+ !in_group_p(inode->i_gid) &&
+ !capable_wrt_inode_uidgid(dir, CAP_FSETID))
+ mode &= ~S_ISGID;
} else
inode->i_gid = current_fsgid();
inode->i_mode = mode;