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From 29c5b8dd6228c4401f034ca0aa85f99ac42cf8dd Mon Sep 17 00:00:00 2001
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From: =?UTF-8?q?Michal=20Sekleta=CC=81r?= <msekleta@redhat.com>
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Date: Thu, 5 Nov 2020 17:55:25 +0100
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Subject: [PATCH] basic/stat-util: make mtime check stricter and use entire
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timestamp
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Note that st_mtime member of struct stat is defined as follows,
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#define st_mtime st_mtim.tv_sec
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Hence we omitted checking nanosecond part of the timestamp (struct
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timespec) and possibly would miss modifications that happened within the
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same second.
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(cherry picked from commit a59b0a9f768f6e27b25f4f1bab6de08842e78d74)
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Related: #1642728
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---
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src/basic/stat-util.c | 22 ++++++++++++++++++++++
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src/basic/stat-util.h | 2 ++
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2 files changed, 24 insertions(+)
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diff --git a/src/basic/stat-util.c b/src/basic/stat-util.c
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index 26aee9bad6..c61c4c0517 100644
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--- a/src/basic/stat-util.c
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+++ b/src/basic/stat-util.c
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@@ -287,3 +287,25 @@ int fd_verify_regular(int fd) {
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return stat_verify_regular(&st);
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}
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+
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+bool stat_inode_unmodified(const struct stat *a, const struct stat *b) {
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+
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+ /* Returns if the specified stat structures reference the same, unmodified inode. This check tries to
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+ * be reasonably careful when detecting changes: we check both inode and mtime, to cater for file
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+ * systems where mtimes are fixed to 0 (think: ostree/nixos type installations). We also check file
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+ * size, backing device, inode type and if this refers to a device not the major/minor.
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+ *
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+ * Note that we don't care if file attributes such as ownership or access mode change, this here is
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+ * about contents of the file. The purpose here is to detect file contents changes, and nothing
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+ * else. */
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+
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+ return a && b &&
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+ (a->st_mode & S_IFMT) != 0 && /* We use the check for .st_mode if the structure was ever initialized */
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+ ((a->st_mode ^ b->st_mode) & S_IFMT) == 0 && /* same inode type */
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+ a->st_mtim.tv_sec == b->st_mtim.tv_sec &&
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+ a->st_mtim.tv_nsec == b->st_mtim.tv_nsec &&
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+ (!S_ISREG(a->st_mode) || a->st_size == b->st_size) && /* if regular file, compare file size */
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+ a->st_dev == b->st_dev &&
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+ a->st_ino == b->st_ino &&
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+ (!(S_ISCHR(a->st_mode) || S_ISBLK(a->st_mode)) || a->st_rdev == b->st_rdev); /* if device node, also compare major/minor, because we can */
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+}
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\ No newline at end of file
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diff --git a/src/basic/stat-util.h b/src/basic/stat-util.h
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index f8014ed30b..9e1a2b70da 100644
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--- a/src/basic/stat-util.h
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+++ b/src/basic/stat-util.h
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@@ -58,3 +58,5 @@ int path_is_temporary_fs(const char *path);
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int stat_verify_regular(const struct stat *st);
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int fd_verify_regular(int fd);
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+
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+bool stat_inode_unmodified(const struct stat *a, const struct stat *b);
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