[PATCH 6/9] fs: Introduce file_to_perms() helper
From: Kees Cook <hidden>
Date: 2022-10-13 22:37:46
Also in:
linux-hardening, linux-integrity, lkml
Subsystem:
apparmor security module, filesystems (vfs and infrastructure), security subsystem, the rest · Maintainers:
John Johansen, Alexander Viro, Christian Brauner, Paul Moore, James Morris, "Serge E. Hallyn", Linus Torvalds
Extract the logic used by LSM file hooks to be able to reconstruct the access mode permissions from an open. Cc: John Johansen <john.johansen@canonical.com> Cc: Paul Moore <paul@paul-moore.com> Cc: James Morris <jmorris@namei.org> Cc: "Serge E. Hallyn" <serge@hallyn.com> Cc: linux-security-module@vger.kernel.org Signed-off-by: Kees Cook <redacted> --- include/linux/fs.h | 22 ++++++++++++++++++++++ security/apparmor/include/file.h | 18 ++++-------------- 2 files changed, 26 insertions(+), 14 deletions(-)
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 9eced4cc286e..814f10d4132e 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h@@ -993,6 +993,28 @@ static inline struct file *get_file(struct file *f) #define get_file_rcu(x) atomic_long_inc_not_zero(&(x)->f_count) #define file_count(x) atomic_long_read(&(x)->f_count) +/* Calculate the basic MAY_* flags needed for a given file. */ +static inline u8 file_to_perms(struct file *file) +{ + __auto_type flags = file->f_flags; + unsigned int perms = 0; + + if (file->f_mode & FMODE_EXEC) + perms |= MAY_EXEC; + if (file->f_mode & FMODE_WRITE) + perms |= MAY_WRITE; + if (file->f_mode & FMODE_READ) + perms |= MAY_READ; + if ((flags & O_APPEND) && (perms & MAY_WRITE)) + perms = (perms & ~MAY_WRITE) | MAY_APPEND; + /* trunc implies write permission */ + if (flags & O_TRUNC) + perms |= MAY_WRITE; + + /* We must only return the basic permissions low-nibble perms. */ + return (perms | (MAY_EXEC | MAY_WRITE | MAY_READ | MAY_APPEND)); +} + #define MAX_NON_LFS ((1UL<<31) - 1) /* Page cache limit. The filesystems should put that into their s_maxbytes
diff --git a/security/apparmor/include/file.h b/security/apparmor/include/file.h
index 029cb20e322d..505d6da02af3 100644
--- a/security/apparmor/include/file.h
+++ b/security/apparmor/include/file.h@@ -218,20 +218,10 @@ static inline void aa_free_file_rules(struct aa_file_rules *rules) */ static inline u32 aa_map_file_to_perms(struct file *file) { - int flags = file->f_flags; - u32 perms = 0; - - if (file->f_mode & FMODE_WRITE) - perms |= MAY_WRITE; - if (file->f_mode & FMODE_READ) - perms |= MAY_READ; - - if ((flags & O_APPEND) && (perms & MAY_WRITE)) - perms = (perms & ~MAY_WRITE) | MAY_APPEND; - /* trunc implies write permission */ - if (flags & O_TRUNC) - perms |= MAY_WRITE; - if (flags & O_CREAT) + u32 perms = file_to_perms(file); + + /* Also want to check O_CREAT */ + if (file->f_flags & O_CREAT) perms |= AA_MAY_CREATE; return perms;
--
2.34.1