From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Return-Path: From: Amir Goldstein Subject: [PATCH 1/2] vfs: replace i_readcount with a biased i_count Date: Sat, 8 Jun 2019 16:57:16 +0300 Message-Id: <20190608135717.8472-2-amir73il@gmail.com> In-Reply-To: <20190608135717.8472-1-amir73il@gmail.com> References: <20190608135717.8472-1-amir73il@gmail.com> To: Miklos Szeredi Cc: "J . Bruce Fields" , Jeff Layton , Mimi Zohar , Al Viro , linux-fsdevel@vger.kernel.org, linux-unionfs@vger.kernel.org, linux-integrity@vger.kernel.org List-ID: Count struct files open RO together with inode reference count instead of using a dedicated i_readcount field. This will allow us to use the RO count also when CONFIG_IMA is not defined and will reduce the size of struct inode for 32bit archs when CONFIG_IMA is defined. We need this RO count for posix leases code, which currently naively checks i_count and d_count in an inaccurate manner. Should regular i_count overflow into RO count bias by struct files opened for write, it's not a big deal, as we mostly need the RO count to be reliable when the first writer comes along. Cc: # v4.19 Signed-off-by: Amir Goldstein --- include/linux/fs.h | 33 +++++++++++++++++++------------ security/integrity/ima/ima_main.c | 2 +- 2 files changed, 21 insertions(+), 14 deletions(-) diff --git a/include/linux/fs.h b/include/linux/fs.h index f7fdfe93e25d..504bf17967dd 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -694,9 +694,6 @@ struct inode { atomic_t i_count; atomic_t i_dio_count; atomic_t i_writecount; -#ifdef CONFIG_IMA - atomic_t i_readcount; /* struct files open RO */ -#endif union { const struct file_operations *i_fop; /* former ->i_op->default_file_ops */ void (*free_inode)(struct inode *); @@ -2890,26 +2887,36 @@ static inline bool inode_is_open_for_write(const struct inode *inode) return atomic_read(&inode->i_writecount) > 0; } -#ifdef CONFIG_IMA +/* + * Count struct files open RO together with inode rerefernce count. + * We need this count for IMA and for posix leases. The RO count should not + * include files opened RDWR nor files opened O_PATH and internal kernel + * inode references, like the ones taken by overlayfs and inotify. + * Should regular i_count overflow into I_RO_COUNT_BIAS by struct files + * opened for write, it's not a big deal, as we mostly need + * inode_is_open_rdonly() to be reliable when the first writer comes along. + */ +#define I_RO_COUNT_SHIFT 10 +#define I_RO_COUNT_BIAS (1UL << I_RO_COUNT_SHIFT) + static inline void i_readcount_dec(struct inode *inode) { - BUG_ON(!atomic_read(&inode->i_readcount)); - atomic_dec(&inode->i_readcount); + WARN_ON(atomic_read(&inode->i_count) < I_RO_COUNT_BIAS); + atomic_sub(I_RO_COUNT_BIAS, &inode->i_count); } static inline void i_readcount_inc(struct inode *inode) { - atomic_inc(&inode->i_readcount); + atomic_add(I_RO_COUNT_BIAS, &inode->i_count); } -#else -static inline void i_readcount_dec(struct inode *inode) +static inline int i_readcount_read(const struct inode *inode) { - return; + return atomic_read(&inode->i_count) >> I_RO_COUNT_SHIFT; } -static inline void i_readcount_inc(struct inode *inode) +static inline bool inode_is_open_rdonly(const struct inode *inode) { - return; + return atomic_read(&inode->i_count) > I_RO_COUNT_BIAS; } -#endif + extern int do_pipe_flags(int *, int); #define __kernel_read_file_id(id) \ diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c index 357edd140c09..766bac778d11 100644 --- a/security/integrity/ima/ima_main.c +++ b/security/integrity/ima/ima_main.c @@ -94,7 +94,7 @@ static void ima_rdwr_violation_check(struct file *file, bool send_tomtou = false, send_writers = false; if (mode & FMODE_WRITE) { - if (atomic_read(&inode->i_readcount) && IS_IMA(inode)) { + if (inode_is_open_rdonly(inode) && IS_IMA(inode)) { if (!iint) iint = integrity_iint_find(inode); /* IMA_MEASURE is set from reader side */ -- 2.17.1