From 426ddeead6112955dfb50ccf9bb4af05d1ca9082 Mon Sep 17 00:00:00 2001 From: Yiannis Marangos Date: Thu, 10 Apr 2014 21:31:21 +0300 Subject: read-cache.c: verify index file before we opportunistically update it Before we proceed to opportunistically update the index (often done by an otherwise read-only operation like "git status" and "git diff" that internally refreshes the index), we must verify that the current index file is the same as the one that we read earlier before we took the lock on it, in order to avoid a possible race. In the example below git-status does "opportunistic update" and git-rebase updates the index, but the race can happen in general. 1. process A calls git-rebase (or does anything that uses the index) 2. process A applies 1st commit 3. process B calls git-status (or does anything that updates the index) 4. process B reads index 5. process A applies 2nd commit 6. process B takes the lock, then overwrites process A's changes. 7. process A applies 3rd commit As an end result the 3rd commit will have a revert of the 2nd commit. When process B takes the lock, it needs to make sure that the index hasn't changed since step 4. Signed-off-by: Yiannis Marangos Signed-off-by: Junio C Hamano --- cache.h | 3 +++ 1 file changed, 3 insertions(+) (limited to 'cache.h') diff --git a/cache.h b/cache.h index ce377e1354..9244c387c3 100644 --- a/cache.h +++ b/cache.h @@ -279,6 +279,7 @@ struct index_state { initialized : 1; struct hash_table name_hash; struct hash_table dir_hash; + unsigned char sha1[20]; }; extern struct index_state the_index; @@ -1199,6 +1200,8 @@ extern void fsync_or_die(int fd, const char *); extern ssize_t read_in_full(int fd, void *buf, size_t count); extern ssize_t write_in_full(int fd, const void *buf, size_t count); +extern ssize_t pread_in_full(int fd, void *buf, size_t count, off_t offset); + static inline ssize_t write_str_in_full(int fd, const char *str) { return write_in_full(fd, str, strlen(str)); -- cgit v1.2.1