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From 53d335085c363f998ab7d81c977704babf2a30e1 Mon Sep 17 00:00:00 2001
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Message-Id: <53d335085c363f998ab7d81c977704babf2a30e1@dist-git>
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From: Eric Blake <eblake@redhat.com>
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Date: Wed, 26 Feb 2014 14:54:36 +0100
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Subject: [PATCH] storage: don't read storage volumes in nonblock mode
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https://bugzilla.redhat.com/show_bug.cgi?id=1032370
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Commit 348b4e2 introduced a potential problem (thankfully not
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in any release): we are attempting to use virFileReadHeaderFD()
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on a file that was opened with O_NONBLOCK. While this
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shouldn't be a problem in practice (because O_NONBLOCK
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typically doesn't affect regular or block files, and fifos and
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sockets cannot be storage volumes), it's better to play it safe
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to avoid races from opening an unexpected file type while also
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avoiding problems with having to handle EAGAIN while read()ing.
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Based on a report by Dan Berrange.
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* src/storage/storage_backend.c
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(virStorageBackendVolOpenCheckMode): Fix up fd after avoiding race.
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Signed-off-by: Eric Blake <eblake@redhat.com>
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(cherry picked from commit 655ea8dc02d88ec742ed2829fafbf6e269002adf)
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Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
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---
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src/storage/storage_backend.c | 25 +++++++++++++++++++++----
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1 file changed, 21 insertions(+), 4 deletions(-)
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diff --git a/src/storage/storage_backend.c b/src/storage/storage_backend.c
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index f8c0004..ae24c74 100644
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--- a/src/storage/storage_backend.c
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+++ b/src/storage/storage_backend.c
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@@ -1150,6 +1150,12 @@ virStorageBackendVolOpenCheckMode(const char *path, struct stat *sb,
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return -2;
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}
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+ /* O_NONBLOCK should only matter during open() for fifos and
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+ * sockets, which we already filtered; but using it prevents a
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+ * TOCTTOU race. However, later on we will want to read() the
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+ * header from this fd, and virFileRead* routines require a
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+ * blocking fd, so fix it up after verifying we avoided a
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+ * race. */
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if ((fd = open(path, O_RDONLY|O_NONBLOCK|O_NOCTTY)) < 0) {
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if ((errno == ENOENT || errno == ELOOP) &&
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S_ISLNK(sb->st_mode)) {
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@@ -1171,13 +1177,13 @@ virStorageBackendVolOpenCheckMode(const char *path, struct stat *sb,
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return -1;
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}
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- if (S_ISREG(sb->st_mode))
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+ if (S_ISREG(sb->st_mode)) {
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mode = VIR_STORAGE_VOL_OPEN_REG;
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- else if (S_ISCHR(sb->st_mode))
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+ } else if (S_ISCHR(sb->st_mode)) {
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mode = VIR_STORAGE_VOL_OPEN_CHAR;
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- else if (S_ISBLK(sb->st_mode))
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+ } else if (S_ISBLK(sb->st_mode)) {
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mode = VIR_STORAGE_VOL_OPEN_BLOCK;
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- else if (S_ISDIR(sb->st_mode)) {
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+ } else if (S_ISDIR(sb->st_mode)) {
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mode = VIR_STORAGE_VOL_OPEN_DIR;
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if (STREQ(base, ".") ||
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@@ -1186,6 +1192,17 @@ virStorageBackendVolOpenCheckMode(const char *path, struct stat *sb,
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VIR_INFO("Skipping special dir '%s'", base);
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return -2;
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}
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+ } else {
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+ VIR_WARN("ignoring unexpected type for file '%s'", path);
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+ VIR_FORCE_CLOSE(fd);
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+ return -2;
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+ }
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+
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+ if (virSetBlocking(fd, true) < 0) {
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+ virReportSystemError(errno, _("unable to set blocking mode for '%s'"),
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+ path);
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+ VIR_FORCE_CLOSE(fd);
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+ return -2;
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}
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if (!(mode & flags)) {
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--
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1.9.0
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