Blame SOURCES/kvm-virtiofsd-passthrough_ll-create-new-files-in-caller-.patch

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From af14ef1dba9356e566c9c7531b8fd23361c2b16d Mon Sep 17 00:00:00 2001
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From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
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Date: Mon, 27 Jan 2020 19:01:12 +0100
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Subject: [PATCH 041/116] virtiofsd: passthrough_ll: create new files in
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 caller's context
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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RH-Author: Dr. David Alan Gilbert <dgilbert@redhat.com>
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Message-id: <20200127190227.40942-38-dgilbert@redhat.com>
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Patchwork-id: 93488
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O-Subject: [RHEL-AV-8.2 qemu-kvm PATCH 037/112] virtiofsd: passthrough_ll: create new files in caller's context
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Bugzilla: 1694164
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RH-Acked-by: Philippe Mathieu-Daudé <philmd@redhat.com>
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RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
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RH-Acked-by: Sergio Lopez Pascual <slp@redhat.com>
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From: Vivek Goyal <vgoyal@redhat.com>
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We need to create files in the caller's context. Otherwise after
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creating a file, the caller might not be able to do file operations on
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that file.
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Changed effective uid/gid to caller's uid/gid, create file and then
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switch back to uid/gid 0.
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Use syscall(setresuid, ...) otherwise glibc does some magic to change EUID
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in all threads, which is not what we want.
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Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
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Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
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Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
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(cherry picked from commit 929cfb7a9a1b101cdfc9ac19807ecab4c81a13e4)
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Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
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---
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 tools/virtiofsd/passthrough_ll.c | 96 +++++++++++++++++++++++++++++++++++++---
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 1 file changed, 91 insertions(+), 5 deletions(-)
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diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c
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index cd27c09..5e06179 100644
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--- a/tools/virtiofsd/passthrough_ll.c
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+++ b/tools/virtiofsd/passthrough_ll.c
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@@ -50,6 +50,7 @@
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 #include <stdlib.h>
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 #include <string.h>
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 #include <sys/file.h>
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+#include <sys/syscall.h>
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 #include <sys/xattr.h>
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 #include <unistd.h>
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@@ -83,6 +84,11 @@ struct lo_inode {
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     uint64_t refcount; /* protected by lo->mutex */
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 };
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+struct lo_cred {
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+    uid_t euid;
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+    gid_t egid;
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+};
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+
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 enum {
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     CACHE_NEVER,
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     CACHE_NORMAL,
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@@ -383,6 +389,69 @@ static void lo_lookup(fuse_req_t req, fuse_ino_t parent, const char *name)
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     }
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 }
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+/*
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+ * On some archs, setres*id is limited to 2^16 but they
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+ * provide setres*id32 variants that allow 2^32.
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+ * Others just let setres*id do 2^32 anyway.
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+ */
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+#ifdef SYS_setresgid32
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+#define OURSYS_setresgid SYS_setresgid32
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+#else
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+#define OURSYS_setresgid SYS_setresgid
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+#endif
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+
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+#ifdef SYS_setresuid32
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+#define OURSYS_setresuid SYS_setresuid32
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+#else
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+#define OURSYS_setresuid SYS_setresuid
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+#endif
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+
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+/*
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+ * Change to uid/gid of caller so that file is created with
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+ * ownership of caller.
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+ * TODO: What about selinux context?
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+ */
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+static int lo_change_cred(fuse_req_t req, struct lo_cred *old)
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+{
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+    int res;
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+
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+    old->euid = geteuid();
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+    old->egid = getegid();
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+
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+    res = syscall(OURSYS_setresgid, -1, fuse_req_ctx(req)->gid, -1);
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+    if (res == -1) {
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+        return errno;
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+    }
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+
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+    res = syscall(OURSYS_setresuid, -1, fuse_req_ctx(req)->uid, -1);
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+    if (res == -1) {
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+        int errno_save = errno;
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+
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+        syscall(OURSYS_setresgid, -1, old->egid, -1);
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+        return errno_save;
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+    }
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+
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+    return 0;
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+}
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+
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+/* Regain Privileges */
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+static void lo_restore_cred(struct lo_cred *old)
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+{
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+    int res;
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+
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+    res = syscall(OURSYS_setresuid, -1, old->euid, -1);
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+    if (res == -1) {
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+        fuse_log(FUSE_LOG_ERR, "seteuid(%u): %m\n", old->euid);
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+        exit(1);
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+    }
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+
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+    res = syscall(OURSYS_setresgid, -1, old->egid, -1);
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+    if (res == -1) {
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+        fuse_log(FUSE_LOG_ERR, "setegid(%u): %m\n", old->egid);
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+        exit(1);
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+    }
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+}
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+
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 static void lo_mknod_symlink(fuse_req_t req, fuse_ino_t parent,
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                              const char *name, mode_t mode, dev_t rdev,
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                              const char *link)
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@@ -391,12 +460,21 @@ static void lo_mknod_symlink(fuse_req_t req, fuse_ino_t parent,
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     int saverr;
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     struct lo_inode *dir = lo_inode(req, parent);
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     struct fuse_entry_param e;
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+    struct lo_cred old = {};
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     saverr = ENOMEM;
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+    saverr = lo_change_cred(req, &old;;
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+    if (saverr) {
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+        goto out;
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+    }
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+
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     res = mknod_wrapper(dir->fd, name, link, mode, rdev);
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     saverr = errno;
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+
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+    lo_restore_cred(&old;;
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+
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     if (res == -1) {
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         goto out;
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     }
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@@ -794,26 +872,34 @@ static void lo_create(fuse_req_t req, fuse_ino_t parent, const char *name,
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     struct lo_data *lo = lo_data(req);
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     struct fuse_entry_param e;
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     int err;
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+    struct lo_cred old = {};
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     if (lo_debug(req)) {
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         fuse_log(FUSE_LOG_DEBUG, "lo_create(parent=%" PRIu64 ", name=%s)\n",
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                  parent, name);
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     }
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+    err = lo_change_cred(req, &old;;
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+    if (err) {
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+        goto out;
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+    }
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+
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     fd = openat(lo_fd(req, parent), name, (fi->flags | O_CREAT) & ~O_NOFOLLOW,
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                 mode);
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-    if (fd == -1) {
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-        return (void)fuse_reply_err(req, errno);
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-    }
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+    err = fd == -1 ? errno : 0;
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+    lo_restore_cred(&old;;
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-    fi->fh = fd;
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+    if (!err) {
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+        fi->fh = fd;
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+        err = lo_do_lookup(req, parent, name, &e);
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+    }
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     if (lo->cache == CACHE_NEVER) {
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         fi->direct_io = 1;
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     } else if (lo->cache == CACHE_ALWAYS) {
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         fi->keep_cache = 1;
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     }
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-    err = lo_do_lookup(req, parent, name, &e);
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+out:
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     if (err) {
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         fuse_reply_err(req, err);
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     } else {
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-- 
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1.8.3.1
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