From d67c0bf0caf26358f5345d6c0ac039026c46bd1e Mon Sep 17 00:00:00 2001 From: Aleksa Sarai Date: Fri, 22 Apr 2016 20:36:43 +1000 Subject: [PATCH] libcontainer: user: always treat numeric ids numerically Most shadow-related tools don't treat numeric ids as potential usernames, so change our behaviour to match that. Previously, using an explicit specification like 111:222 could result in the UID and GID not being 111 and 222 respectively (which is confusing). Some of the code was quite confusing inside libcontainer/user, so refactor and comment it so future maintainers can understand what's going and what edge cases we have to deal with. This fixes CVE-2016-3697. Signed-off-by: Aleksa Sarai --- .../runc/libcontainer/user/lookup.go | 3 + .../opencontainers/runc/libcontainer/user/user.go | 149 ++++++++++++--------- 2 files changed, 89 insertions(+), 63 deletions(-) diff --git a/vendor/src/github.com/opencontainers/runc/libcontainer/user/lookup.go b/vendor/src/github.com/opencontainers/runc/libcontainer/user/lookup.go index 6f8a982..7062940 100644 --- a/vendor/src/github.com/opencontainers/runc/libcontainer/user/lookup.go +++ b/vendor/src/github.com/opencontainers/runc/libcontainer/user/lookup.go @@ -9,6 +9,9 @@ import ( var ( // The current operating system does not provide the required data for user lookups. ErrUnsupported = errors.New("user lookup: operating system does not provide passwd-formatted data") + // No matching entries found in file. + ErrNoPasswdEntries = errors.New("no matching entries in passwd file") + ErrNoGroupEntries = errors.New("no matching entries in group file") ) func lookupUser(filter func(u User) bool) (User, error) { diff --git a/vendor/src/github.com/opencontainers/runc/libcontainer/user/user.go b/vendor/src/github.com/opencontainers/runc/libcontainer/user/user.go index e6375ea..43fd39e 100644 --- a/vendor/src/github.com/opencontainers/runc/libcontainer/user/user.go +++ b/vendor/src/github.com/opencontainers/runc/libcontainer/user/user.go @@ -15,7 +15,7 @@ const ( ) var ( - ErrRange = fmt.Errorf("Uids and gids must be in range %d-%d", minId, maxId) + ErrRange = fmt.Errorf("uids and gids must be in range %d-%d", minId, maxId) ) type User struct { @@ -42,29 +42,30 @@ func parseLine(line string, v ...interface{}) { parts := strings.Split(line, ":") for i, p := range parts { + // Ignore cases where we don't have enough fields to populate the arguments. + // Some configuration files like to misbehave. if len(v) <= i { - // if we have more "parts" than we have places to put them, bail for great "tolerance" of naughty configuration files break } + // Use the type of the argument to figure out how to parse it, scanf() style. + // This is legit. switch e := v[i].(type) { case *string: - // "root", "adm", "/bin/bash" *e = p case *int: - // "0", "4", "1000" - // ignore string to int conversion errors, for great "tolerance" of naughty configuration files + // "numbers", with conversion errors ignored because of some misbehaving configuration files. *e, _ = strconv.Atoi(p) case *[]string: - // "", "root", "root,adm,daemon" + // Comma-separated lists. if p != "" { *e = strings.Split(p, ",") } else { *e = []string{} } default: - // panic, because this is a programming/logic error, not a runtime one - panic("parseLine expects only pointers! argument " + strconv.Itoa(i) + " is not a pointer!") + // Someone goof'd when writing code using this function. Scream so they can hear us. + panic(fmt.Sprintf("parseLine only accepts {*string, *int, *[]string} as arguments! %#v is not a pointer!", e)) } } } @@ -106,8 +107,8 @@ func ParsePasswdFilter(r io.Reader, filter func(User) bool) ([]User, error) { return nil, err } - text := strings.TrimSpace(s.Text()) - if text == "" { + line := strings.TrimSpace(s.Text()) + if line == "" { continue } @@ -117,10 +118,7 @@ func ParsePasswdFilter(r io.Reader, filter func(User) bool) ([]User, error) { // root:x:0:0:root:/root:/bin/bash // adm:x:3:4:adm:/var/adm:/bin/false p := User{} - parseLine( - text, - &p.Name, &p.Pass, &p.Uid, &p.Gid, &p.Gecos, &p.Home, &p.Shell, - ) + parseLine(line, &p.Name, &p.Pass, &p.Uid, &p.Gid, &p.Gecos, &p.Home, &p.Shell) if filter == nil || filter(p) { out = append(out, p) @@ -135,6 +133,7 @@ func ParseGroupFile(path string) ([]Group, error) { if err != nil { return nil, err } + defer group.Close() return ParseGroup(group) } @@ -178,10 +177,7 @@ func ParseGroupFilter(r io.Reader, filter func(Group) bool) ([]Group, error) { // root:x:0:root // adm:x:4:root,adm,daemon p := Group{} - parseLine( - text, - &p.Name, &p.Pass, &p.Gid, &p.List, - ) + parseLine(text, &p.Name, &p.Pass, &p.Gid, &p.List) if filter == nil || filter(p) { out = append(out, p) @@ -192,9 +188,10 @@ func ParseGroupFilter(r io.Reader, filter func(Group) bool) ([]Group, error) { } type ExecUser struct { - Uid, Gid int - Sgids []int - Home string + Uid int + Gid int + Sgids []int + Home string } // GetExecUserPath is a wrapper for GetExecUser. It reads data from each of the @@ -235,12 +232,12 @@ func GetExecUserPath(userSpec string, defaults *ExecUser, passwdPath, groupPath // * "uid:gid // * "user:gid" // * "uid:group" +// +// It should be noted that if you specify a numeric user or group id, they will +// not be evaluated as usernames (only the metadata will be filled). So attempting +// to parse a user with user.Name = "1337" will produce the user with a UID of +// 1337. func GetExecUser(userSpec string, defaults *ExecUser, passwd, group io.Reader) (*ExecUser, error) { - var ( - userArg, groupArg string - name string - ) - if defaults == nil { defaults = new(ExecUser) } @@ -258,87 +255,113 @@ func GetExecUser(userSpec string, defaults *ExecUser, passwd, group io.Reader) ( user.Sgids = []int{} } - // allow for userArg to have either "user" syntax, or optionally "user:group" syntax + // Allow for userArg to have either "user" syntax, or optionally "user:group" syntax + var userArg, groupArg string parseLine(userSpec, &userArg, &groupArg) + // Convert userArg and groupArg to be numeric, so we don't have to execute + // Atoi *twice* for each iteration over lines. + uidArg, uidErr := strconv.Atoi(userArg) + gidArg, gidErr := strconv.Atoi(groupArg) + + // Find the matching user. users, err := ParsePasswdFilter(passwd, func(u User) bool { if userArg == "" { + // Default to current state of the user. return u.Uid == user.Uid } - return u.Name == userArg || strconv.Itoa(u.Uid) == userArg + + if uidErr == nil { + // If the userArg is numeric, always treat it as a UID. + return uidArg == u.Uid + } + + return u.Name == userArg }) + + // If we can't find the user, we have to bail. if err != nil && passwd != nil { if userArg == "" { userArg = strconv.Itoa(user.Uid) } - return nil, fmt.Errorf("Unable to find user %v: %v", userArg, err) + return nil, fmt.Errorf("unable to find user %s: %v", userArg, err) } - haveUser := users != nil && len(users) > 0 - if haveUser { - // if we found any user entries that matched our filter, let's take the first one as "correct" - name = users[0].Name + var matchedUserName string + if len(users) > 0 { + // First match wins, even if there's more than one matching entry. + matchedUserName = users[0].Name user.Uid = users[0].Uid user.Gid = users[0].Gid user.Home = users[0].Home } else if userArg != "" { - // we asked for a user but didn't find them... let's check to see if we wanted a numeric user - user.Uid, err = strconv.Atoi(userArg) - if err != nil { - // not numeric - we have to bail - return nil, fmt.Errorf("Unable to find user %v", userArg) + // If we can't find a user with the given username, the only other valid + // option is if it's a numeric username with no associated entry in passwd. + + if uidErr != nil { + // Not numeric. + return nil, fmt.Errorf("unable to find user %s: %v", userArg, ErrNoPasswdEntries) } + user.Uid = uidArg // Must be inside valid uid range. if user.Uid < minId || user.Uid > maxId { return nil, ErrRange } - // if userArg couldn't be found in /etc/passwd but is numeric, just roll with it - this is legit + // Okay, so it's numeric. We can just roll with this. } - if groupArg != "" || name != "" { + // On to the groups. If we matched a username, we need to do this because of + // the supplementary group IDs. + if groupArg != "" || matchedUserName != "" { groups, err := ParseGroupFilter(group, func(g Group) bool { - // Explicit group format takes precedence. - if groupArg != "" { - return g.Name == groupArg || strconv.Itoa(g.Gid) == groupArg + // If the group argument isn't explicit, we'll just search for it. + if groupArg == "" { + // Check if user is a member of this group. + for _, u := range g.List { + if u == matchedUserName { + return true + } + } + return false } - // Check if user is a member. - for _, u := range g.List { - if u == name { - return true - } + if gidErr == nil { + // If the groupArg is numeric, always treat it as a GID. + return gidArg == g.Gid } - return false + return g.Name == groupArg }) if err != nil && group != nil { - return nil, fmt.Errorf("Unable to find groups for user %v: %v", users[0].Name, err) + return nil, fmt.Errorf("unable to find groups for spec %v: %v", matchedUserName, err) } - haveGroup := groups != nil && len(groups) > 0 + // Only start modifying user.Gid if it is in explicit form. if groupArg != "" { - if haveGroup { - // if we found any group entries that matched our filter, let's take the first one as "correct" + if len(groups) > 0 { + // First match wins, even if there's more than one matching entry. user.Gid = groups[0].Gid - } else { - // we asked for a group but didn't find id... let's check to see if we wanted a numeric group - user.Gid, err = strconv.Atoi(groupArg) - if err != nil { - // not numeric - we have to bail - return nil, fmt.Errorf("Unable to find group %v", groupArg) + } else if groupArg != "" { + // If we can't find a group with the given name, the only other valid + // option is if it's a numeric group name with no associated entry in group. + + if gidErr != nil { + // Not numeric. + return nil, fmt.Errorf("unable to find group %s: %v", groupArg, ErrNoGroupEntries) } + user.Gid = gidArg - // Ensure gid is inside gid range. + // Must be inside valid gid range. if user.Gid < minId || user.Gid > maxId { return nil, ErrRange } - // if groupArg couldn't be found in /etc/group but is numeric, just roll with it - this is legit + // Okay, so it's numeric. We can just roll with this. } - } else if haveGroup { - // If implicit group format, fill supplementary gids. + } else if len(groups) > 0 { + // Supplementary group ids only make sense if in the implicit form. user.Sgids = make([]int, len(groups)) for i, group := range groups { user.Sgids[i] = group.Gid -- 2.8.1