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fs: fix race condition in get/set security descriptor

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Calling `Load()` twice for an atomic variable can return different
values each time. This resulted in trying to read the security
descriptor with high privileges, but then not entering the code path to
switch to low privileges when another thread has already done so
concurrently.
This commit is contained in:
Michael Eischer 2024-08-26 19:31:21 +02:00
parent 1931beab8e
commit 6fbfccc2d3
1 changed files with 8 additions and 4 deletions
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12
internal/fs/sd_windows.go
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@ -48,13 +48,15 @@ func GetSecurityDescriptor(filePath string) (securityDescriptor *[]byte, err err
var sd *windows.SECURITY_DESCRIPTOR var sd *windows.SECURITY_DESCRIPTOR
if lowerPrivileges.Load() { // store original value to avoid unrelated changes in the error check
useLowerPrivileges := lowerPrivileges.Load()
if useLowerPrivileges {
sd, err = getNamedSecurityInfoLow(filePath) sd, err = getNamedSecurityInfoLow(filePath)
} else { } else {
sd, err = getNamedSecurityInfoHigh(filePath) sd, err = getNamedSecurityInfoHigh(filePath)
} }
if err != nil { if err != nil {
if !lowerPrivileges.Load() && isHandlePrivilegeNotHeldError(err) { if !useLowerPrivileges && isHandlePrivilegeNotHeldError(err) {
// If ERROR_PRIVILEGE_NOT_HELD is encountered, fallback to backups/restores using lower non-admin privileges. // If ERROR_PRIVILEGE_NOT_HELD is encountered, fallback to backups/restores using lower non-admin privileges.
lowerPrivileges.Store(true) lowerPrivileges.Store(true)
sd, err = getNamedSecurityInfoLow(filePath) sd, err = getNamedSecurityInfoLow(filePath)
@ -109,14 +111,16 @@ func SetSecurityDescriptor(filePath string, securityDescriptor *[]byte) error {
sacl = nil sacl = nil
} }
if lowerPrivileges.Load() { // store original value to avoid unrelated changes in the error check
useLowerPrivileges := lowerPrivileges.Load()
if useLowerPrivileges {
err = setNamedSecurityInfoLow(filePath, dacl) err = setNamedSecurityInfoLow(filePath, dacl)
} else { } else {
err = setNamedSecurityInfoHigh(filePath, owner, group, dacl, sacl) err = setNamedSecurityInfoHigh(filePath, owner, group, dacl, sacl)
} }
if err != nil { if err != nil {
if !lowerPrivileges.Load() && isHandlePrivilegeNotHeldError(err) { if !useLowerPrivileges && isHandlePrivilegeNotHeldError(err) {
// If ERROR_PRIVILEGE_NOT_HELD is encountered, fallback to backups/restores using lower non-admin privileges. // If ERROR_PRIVILEGE_NOT_HELD is encountered, fallback to backups/restores using lower non-admin privileges.
lowerPrivileges.Store(true) lowerPrivileges.Store(true)
err = setNamedSecurityInfoLow(filePath, dacl) err = setNamedSecurityInfoLow(filePath, dacl)