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activation: Lock /etc/.pwd.lock before accessing databases. 

Suggested by Florian Pelz <pelzflorian@pelzflorian.de>
in <http://bugs.gnu.org/35996>.

* gnu/build/accounts.scm (%password-lock-file): New variable.
* gnu/build/activation.scm (activate-users+groups): Wrap calls to
'user+group-databases', 'write-group', etc. into 'with-file-lock'.
This commit is contained in:
Ludovic Courtès 2019-06-03 17:14:17 +02:00
parent 5f0cf1df71
commit d497b6ab39
No known key found for this signature in database
GPG Key ID: 090B11993D9AEBB5
2 changed files with 25 additions and 14 deletions
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6
gnu/build/accounts.scm
View File

@ -51,6 +51,7 @@
group-entry-gid group-entry-gid
group-entry-members group-entry-members
%password-lock-file
write-group write-group
write-passwd write-passwd
write-shadow write-shadow
@ -224,6 +225,11 @@ each field."
(serialization list->comma-separated comma-separated->list) (serialization list->comma-separated comma-separated->list)
(default '()))) (default '())))
(define %password-lock-file
;; The password database lock file used by libc's 'lckpwdf'. Users should
;; grab this lock with 'with-file-lock' when they access the databases.
"/etc/.pwd.lock")
(define (database-writer file mode entry->string) (define (database-writer file mode entry->string)
(lambda* (entries #:optional (file-or-port file)) (lambda* (entries #:optional (file-or-port file))
"Write ENTRIES to FILE-OR-PORT. When FILE-OR-PORT is a file name, write "Write ENTRIES to FILE-OR-PORT. When FILE-OR-PORT is a file name, write

9
gnu/build/activation.scm
View File

@ -22,6 +22,7 @@
#:use-module (gnu build accounts) #:use-module (gnu build accounts)
#:use-module (gnu build linux-boot) #:use-module (gnu build linux-boot)
#:use-module (guix build utils) #:use-module (guix build utils)
#:use-module ((guix build syscalls) #:select (with-file-lock))
#:use-module (ice-9 ftw) #:use-module (ice-9 ftw)
#:use-module (ice-9 match) #:use-module (ice-9 match)
#:use-module (ice-9 vlist) #:use-module (ice-9 vlist)
@ -129,11 +130,15 @@ group records) are all available."
;; Allow home directories to be created under /var/lib. ;; Allow home directories to be created under /var/lib.
(mkdir-p "/var/lib") (mkdir-p "/var/lib")
;; Take same lock as libc's 'lckpwdf' (but without a timeout) while we read
;; and write the databases. This ensures there's no race condition with
;; other tools that might be accessing it at the same time.
(with-file-lock %password-lock-file
(let-values (((groups passwd shadow) (let-values (((groups passwd shadow)
(user+group-databases users groups))) (user+group-databases users groups)))
(write-group groups) (write-group groups)
(write-passwd passwd) (write-passwd passwd)
(write-shadow shadow) (write-shadow shadow)))
;; Home directories of non-system accounts are created by ;; Home directories of non-system accounts are created by
;; 'activate-user-home'. ;; 'activate-user-home'.
@ -144,7 +149,7 @@ group records) are all available."
(for-each (lambda (directory) (for-each (lambda (directory)
(chown directory 0 0) (chown directory 0 0)
(chmod directory #o555)) (chmod directory #o555))
(duplicates (map user-account-home-directory system-accounts))))) (duplicates (map user-account-home-directory system-accounts))))
(define (activate-user-home users) (define (activate-user-home users)
"Create and populate the home directory of USERS, a list of tuples, unless "Create and populate the home directory of USERS, a list of tuples, unless